Goku was determined to train Gohan - to make him the best descendant he possibly can be. The boy was exhausted at the end of every session, but Goku knew he had hidden potential, the power of a super saiyan. Maybe it was too early yet, but he wants to unlock that in him through strenuous training. 
The two had camped out at a mountain trail for the night, where Goku was eager to test Gohan’s strength against the winds.
Though at times he wavered, Gohan had a heart of conviction - and it made his father proud. 
The two were now sweating and exasperated from their training, and Goku clapped him on the back. 
“You did a great job back there, Gohan!”
After catching his breath, Gohan giggled out happily. 
“Thanks a lot, dad!”
For being 11 years old, Gohan is definitely a strong boy from his constant training with father. No doubt that would serve him well in the battles to come. 
Both males were dripping in sweat, the two of them exhausted from their training.
The boy looked over his father's muscular rippled form and blushed. He doesn't want to admit it, but looking at his father always made him feel funny between his legs.
Goku looked sideways at Gohan and smiled. 
“It's time we get a bath - isn't it, son?”
Gohan stopped gawking and nodded. 
“Come this way, follow me. There's a hot spring nearby.”
Gohan took his father's hand and followed him down the cave in the mountain, to a hot spring. 
Once there, Gohan felt the heat of the spring wash over his face and body - a welcome change from the cold air of the mountain - sweeping away the sweat residue on his body. 
His father was stripping down to his bare skin already, and Gohan quickly did the same - eager to jump in the spring and get himself cleaned up. 
At random intervals, he would sneak a peek at Goku’s raw, muscular form and feel that same funny feeling between his legs.
“I should ask dad about it…” He thought idly. 
Goku was beckoning him into the water, and Gohan couldn't help but stare at that muscled chest for a moment before jumping in, the water not causing nearly as large as an effect as what happened when his father dived in. 
“I guess it's all that muscle,” Gohan murmured under his breath.
Once in the water, Gohan splashed around a little, before his father locked him in a gruff headlock from behind. 
Creating sudden contact his father awakened that feeling inside him again, and Gohan was started to get shivers up his spine as Goku whispered into his ear. 
“What's up, son? You seem to be acting strange lately.”
Gohan gulped and tried to look away from his father, 
“U-Uhm it's nothing dad, I'm just a bit tired from the training…”
Goku took a deep breath and embraced his son camly, kissing him on the cheek. Those muscular arms felt really nice around Gohan’s smaller, chubbier, and lithe body. 
“Of course. You must be worn out so we'll stop playing for now. Go and relax!” 
Gohan meekly nodded and watched his father swim over to the other side of the spring. 
Although the steam rising up made it hard to discern what was going on below the water, he could tell his penis got a little stiff, and bit his lip. 
“What if dad notices I like him in a weird way?”
He closed his eyes and shook his head. 
“No. All that matters is my training and getting myself clean.”

--Meanwhile, on the other side of the spring--

Goku was using his time at the springs as a time of meditation, but something prevented him from achieving true zen… Even though his son's change in attitude worried him, it felt like something personal, something to do with him. 
He opened one eye, and looked down to see his huge uncut cock poking out the water. He gasped, face flushed and turned around from his son, which thankfully still had his back to him - paddling along happily, and taking in the heat of the spring. 
“So that's what is going on…” He whispered to himself, his cock still fully erect and throbbing. 
It's true that Goku hasn't had much time to himself recently - taking care of his son was a lot of hard work, so much so, that he had completely forgot about his sexual urges… Until now. 
Goku sighed, his head was swimming with lust, and his thick uncut cock begged to be stroked. His balls felt really heavy too - churning along with cum. 
There's no way he can bust a nut here out in the water. He'd have to find another way. 
To make matters worse, his cock simply refused to go down. 
He would have to distract himself by cleaning, if he was to come out of the spring without surprising his son… 

--Back to Gohan’s side of the spring--

Gohan was rarely alone with his thoughts since his father was always accompanying him. But, today, it seemed like his head is becoming a mess with these new-found feelings. 
Gohan felt disgusted that he gets so flustered by his father, his muscular body, seeing that handsome face smile… 
He closed his eyes and shook his head again, trying to shake this thoughts from his mind physically.
At the very least, the hot spring had been relaxing his nerves somewhat. Not enough, though… 
With each moment he spent with his father, the feelings only seemed to get stronger. He couldn't bottle it up all the time… Gohan wanted a time and place to tell him. 

The heavy splashing of water darted him out from his thoughts, and he turned around to see his father walking up to him, smiling at him. 
With such a handsome and contagious smile like that, Gohan couldn't help but beam back at his father. 
Once his father reached his location, he put his large hand on his Gohan’s shoulder, causing him to jump out in surprise. 
Goku was about to say something, but he chuckled. 
“You really need to get used to physical contact, Gohan…”
Gohan dropped his head down and mumbled apologies, but his eyes shot open once he saw the start of his dad's shaft. 
Goku looked inquisitively at his son, 
“What has got you so worked up, Gohan? You have been acting really strange lately.” Goku followed his son's eyesight and he noticed it too. 
“O-Oh, um… Don't worry about that. I'm pretty tall, so my… member is bound to say hello, emerging from the water. Um, Gohan you can look up now…”
“Oh! Sorry father… I'm just really hungry.”
Goki blushed and his throat dried up, 
“Um, ‘hungry’? Hungry for what?” He felt his cock twitching to life, that low hanger getting ever stiffer. 
Gohan frowned, and looked his father straight in the eyes - trying to ignore his dad's thick piece of meat to the best of his ability.
“For food, father.” He said, already pacing out of the spring, picking up his clothes, and heading back to camp. 
Goku sighed and mentally scolded himself. 
“I'm some kind of perv, thinking that my son is hungry for cock… But, then again, I am really horny.”

---Back at the cliffside camp---

Goku smiled and tended to the burning fire, looking across at the sunset. 
“The view is so great from here…” He mumbled out. 
Gohan sat beside him, and picked up his skewered food - hovering it over the fire. 
“I feel so hungry today,” Gohan mused.
“That's because of all the training we've done, son.” 
Gohan frowned as he watched the sun set, munching on his food. 
“Hmm, I'm not sure, this hunger feels a little different from normal hunger.”
Goku chuckled, and took a bite of his meat skewer. 
“I think you're just young and experiencing new things. I wouldn't worry too much”, he said - ruffling Gohan’s hair. 

Goku turned his attention to the full moon, and gasped with surprise as he felt his skin prickle up. 
His son looked at his father worryingly, then Gohan’s eyes widened as he saw how black hair grew from his father's arms. 
For the first time in a while, Gohan was struck with fear. 
“D-Dad, what's happening to you?”
Goku smiled at his son, and closed his eyes. 
“When a full moon occurs, we transform into Oozaru. With it, come special instincts. This is part of your training, Gohan.” 
Gohan gulped and gasped as he felt his skin standing on end - prickling up and feeling tingly. That feeling spread to all over his body, and he could feel himself changing somehow. 
His father's arm was now completely hairy - the black hair thickening to look like fur. Gohan looked down to his hands and feet extending into claws, his face turning into a mix or horror of amazement. 
“F-Father, have we always had this power?!”
Goku deeply chuckled and opened his eyes, now a blazing red. 
“Yes, we have to trust our instincts!” His voice boomed deeply, and his mouth turned into a muzzle - now protruding fangs. 
Gohan watched in awe as his father's muscles bulged to an abnormal size, growing with each second. 
As his father was transforming, so was Gohan himself.
The sinew in his arms separated and bulged out, along with his back - popping out and filling with new energy and a coat of black/brown fur. 
Gohan felt his backside extending slightly, something felt like it was pulling… 
He looked behind himself to see his tail swishing about, and then came the change in his loins! 
It was like that funny feeling he'd get whenever he was around his father, except that this time - his penis felt thicker, longer! 
No part of his body was spared; Gohan was going to become an ape all over, his father too - under the gleaming moonlight. 
He felt something pulling at his backside, his hands forming into paws as the seconds whizzed by. He stroked his paw over his newly-found tail, his heightened sense of touch evidenced by the prickly sensation that his paw picked up from his tail. His sense of smell increased, too. Most notably he smelt his father's heavy, manly, musk in the air. 
Just from that smell of dominance, was enough to send Gohan into submission mode - whimpering lowly, eyes quivering as he watched his father turn into a hulky ape, and his mouth watering as he created eye contact with the eager log between his father's strong legs, that cock throbbing and leak fresh precum on the floor. 

Clothes were being ripped apart, no longer able to fit the transformed ape men - due to their larger size. Goku, in particular, had ripped through his clothes in mere seconds thanks to his already muscular form becoming even more larger. 
Goku’s voice boomed deeply at his son - who was midway through his transformation. 
“Don't worry son, just trust your instincts!”
His voice distorted until nothing intelligible could be made from it, just loud grunts and groans. 
Saliva flinged from his mouth as he roared, his paw tearing off his measly loincloth that barely covered his huge thick cock in the first place. 
Gohan’s eyes widened as he saw that massive uncut black rod waving around - fully erect and dripping precum. 
He whimpered in submission, feeling the fur trickle over his face, his arms, and his body as he looked at his father in awe. Now more than ever, he wanted to serve his father. He wants to feel his body rubbing against him, his cock inside him, his cum swirling around in his stomach… 
Although Gohan had also gained muscle through the transformation, his father was especially bulky in comparison to him - Goku’s black fur looked like it was shining through every muscular crevasse, the big and hard muscles twitching and popping veins all throughout his manly body. He certainly smelt like a man, too. Goku also seemed really horny, as evidenced by those churning balls, fat uncut ape meat waving around, and deep - focused breaths. The anticipation coming from both animals could be felt in the air - one was clearly dominant, and the other, submissive. 
“Son…” Goku’s voice sounded very different now - quite deep and animalistic. 
“I need to breed you. Hard.”
Gohan gulped and bent over his behind for Goku to gawk at. Gohan’s ass was pretty big, thick and furry now. 
He could hear his father licking his lips. 
“I trust you, father. This is for my training… And for me to fully grasp my instincts.” He said in his new voice. 
Gohan could hear Goku’s shaky breaths getting closer to him, stroking his tail which grew out of his behind.

Gohan perked up his fuzzy rump to his father upon hearing those words, and closed his eyes in anticipation.
“This is it,” he thought. “I can finally embrace these desires for my father!” A mix of excitement and nervousness washed over Gohan - though he knows these feelings to be true, and he would very much like his father to mate him, he doesn't have a single idea of how he was going to do that. 
Luckily, though, Gohan doesn't have to do anything - as Goku was already taking control. 
Gohan felt a sharp pain searing through his tailz from it being yanked, and yelped, also feeling the tip of his father's uncut cock brush up on his backside simultaneously. Goku wasn't going to go easy on him, he just knew that. 
Goku whispered into his son's ear like at the hot springs, but he didn't say anything this time - just animalistic grunts. 

Again, Gohan felt that shiver up his spine, but this time it was different. Submissiveness overtook him, a result of his new animal instincts. 
“My hole is yours to breed, father…” He said, feeling his cock erect and leak precum onto the ground.
He felt his muscular lay his strong chest on his back and pant needily into his ear. 
The tip of that fat uncut cock lodged through Gohan’s tight pink ape hole, slicking it up with pre and bursting through in a matter of seconds. This, of course, took Gohan by surprise - but like as any good bitch, he just had to stay down and accept it. 
But Gohan struggled to accept his father's fat uncut tip in at first, though thankfully his submissive instincts were already doing the job for him - his ass relaxing as more and more of that cock was shoved in. 
Meanwhile, the predator in the situation - being his father - was slobbering all over his son's furry shoulder, panting hot breath into his ear, and using all of his energy into his groin, to stab his black, meaty member into his son's quivering,  eager hole. 
Though he cried out a high pitched whimper, nothing could stop Goku from attaining his desires. 
He picked up Gohan in his paws, pounding an extra 3 inches of his shaft in him - that made Gohan cry out in pain. The vibrations, tightness and warmth that rippled over Goku’s massive cock was amazing, and it only spurred him on more to keep thrusting his new bitch into submission. 
Goku had suppressed his sexual desires for far too long - as an ape, it became so unbearable that he simply had to fuck any hole, no matter what. It's a good job his son was so willing. 
The large ape yanked on his son's tail, hiked it up, and grabbed his body on his paws - pulling him up against the grassy stone rock, to get pummeled further by his cock while stood up. His prey was not going to slide around the floor anymore - he was going to stand up, and fuck him fully like a proper alpha. As Gohan’s tail was yanked, he was paralysed in place. This was perfect for the dominant male, as he could use him however he wanted. 
With each thrust, his fat furry balls whacked that plump, smaller ass of his son and created a loud echoing noise from the sheet strength of the thrust. Goku’s balls were like pendulum, and his cock was a club. 
The further he went in his son's ass, the tighter it became. After several short and eager thrusts, Goku finally managed to get balls deep and he felt Gohan’s whole body quivering with delight in his grip. 
He wanted to say something, but all he could do was grunt like an animal - adding to the cacophony of pleasured moans and whimpers from his young bitch. 
That dick was shoved in and out at a blurring speed; Goku’s breathing becoming more and more harsher, along with his grip around his son. 
Meanwhile, Gohan was in bliss - his father's fat ape dick was hitting his prostate everytime, and he became so delirious with pleasure that he could no longer whimper out - just drool on the floor with his eyes half-open. 
Goku’s grunting evolved into loud shouts; the unmistakable sound of animals mating and big thick uncut dick, smashing a small, young and tight hole. 
With a loud roar of dominance, Goku thrusted a final time into his son - those pendulum-like balls stopped swinging and were mushed up that plump sore bottom. His fat long ape cock was gushing out thick wads of cum, going straight into his son’s guts and his bitch had no choice to accept it - seeing as his father was literally pinning him against the rock with nowhere to go. Letting the predatory instincts overtake him, Goku bit on his son’s neck and growled deeply. It caused a bit of pain to Gohan, but - as far as animal hierarchy is concerned - this showed his place beneath his father; to be his little cumdump. 
The deep groaning was turning into light whimpers, and when Goku nuzzled his son's neck, it set Gohan at ease.
As his belly was filled with his father's cum, his whines became less and less apparent - both males now satisfied with their mating period. Gohan broke out into a smile with his father, and felt loved in his embrace, his father's grip softening to stroke through his fur. 
It seems that they both wanted it all along, then.

The afterglow seemed to go on forever - acting as a much needed reprieve from Goku’s rough fucking.
Goku’s huge uncut cock is still firmly erect within his son's ass, gripped with a nice warm tightness. 
He pulled back his cock with a “sclurp” sound, out of that tight and worn-out asshole of his son. With it, cum was flooding back to the floor. Goku definitely filled his son up with weeks worth of pent up cum and it showed.
The cum was thick, goopey, and trickled down Gohan’s shapely rump like syrup. 
Gohan trembled, and he felt the powerful feeling in his loins more than ever before. Goku noticed this and wrapped his paws around his son’s throbbing meat. He felt precum flowing down his paws; his son was horny, and he hasn’t got off yet. 
Wordlessly, he retreated from behind Gohan and guided him down on the rock.
Gohan looked up at him curiously, but what diverted most of Goku’s attention was that throbbing, big uncut cock, quite impressive for an 11 year old - and that’s when Goku knew that his son took after his father in more ways than one.
For one, his footpaw was very big - and covered over his son's whole cock, causing great pleasure to his son. 
Goku smirked as he saw his son whimper and groan under his powerful foot, using his furry toes to massage that cock and spreading them apart to reach all sides of the shaft. 
Gohan was overcome by pleasure. 
Even if his dad wasn't fucking him, he was finding at least one way to dominate him - and that furry, soft, warm, and huge foot was irresistible. Gohan gave into its pleasure, and shivers ran up his spine as his penis got the worship it deserved from his father's foot. 
There were multiple ways to make pleasure to a penis, and it was more than just a simple blowjob or a quick hole to blow in. It was about trusting each other, that his son put his faith in his father to not hurt his penis with his foot - but rather, pleasure it in the best way possible. 
He loved the liberating feeling that occurred whenever Goku parted his huge toes to stroke his whole cock entirely between the gap. His father's smooth foot felt like a blanket, and that fur tickled the fire of lust within him. 
Gohan was ready to show his father just how much he loved him. His pleasure, his training, his urges… Its all because of him. 
Growling out menacingly for the first time in his life, Gohan came all over Goku’s footpaw as it rubbed against his member - coating those brown furry toes with a thick layer of white cum, and smearing his smooth underfoot with it too.
The orgasm overtook him like a wave; it was the best one he's ever experienced, thanks to his father. 
Gohan closed his fiery ember eyes, and cooed out in that warm embrace the foot was causing. He could feel his still-cumming cock throb against it and make a mess as his father's foot moved. 
Then, after a full minute, his orgasm finally subsided and he opened his eyes to see his father looking at him lovingly. 
His bulky arms extended down to reach him, and his father picked him up and walked around with him to the cliff's edge. Gohan felt comforted by his father's muscular arms and his warm embrace. His chest emanated a deep musk that sent him to sleep. 
Suddenly, his deep voice reverberated in his chest:
“This is where we sleep, son.” 
Gohan was set down on his father's cozy lap, and he felt himself falling asleep, hearing and feeling his father's muscular chest rising and falling in tandem with his breathing. 
Goku looked across the horizon as his son was falling asleep from his warm embrace - the sun was rising, and his eyes faded to warmth, the burning desire of lust was gone from his eyes - for now, at least.
Goku, too, felt himself falling asleep - from the amazing fuck he just had, no doubt!

---The Next Morning---

The two are laying on the grass, now back to their original human forms. 
Their tails were still remaining despite the transformation back - maybe it was a sign to show that they has mastered their instincts fully. Their two tails intertwined together as they slept under the bright morning sun. The first to awaken was Gohan, grumbling awake and then rubbing his eyes - only to notice that his paws didn't feel furry anymore. 
Gohan audibly gasped as he set sight on his human body once again. 
“...What happened last night?” Doubt set in his mind, but Goku’s still-visible tail confirmed his suspicions: his father really did fuck him last night. His belly was sloshing with cum, his rump was sore and - to top it off - there was a bite mark on his neck. But Gohan felt happy. It really was amazing, and it was what he was wanting all along. 
Giggling with excitement, he shook his father awake and Goku looked at him apologetically. 
“Ah, son…” He said, sitting up and stretching - the muscles popping and rippling all over his body. 
“Damn, my dad is so hot, even if he's not a horny ape…” Gohan thought. His dad looked him straight in the eye, and cupped his chin. 
“Did you like it last night?” He said sternly. 
Gohan broke out into a warm smile, and felt his tail intertwining with his father's. 
“I loved every single minute of it, daddy.” He said, with confidence, reaching in closer to kiss his father on the lips. 
Once he pulled back, Goku blushed heavily and tried to ignore the throbbing in his loins. 
“Ah, I see…” Gohan sighed, and rested his back down onto the grass. He closed his eyes and smiled, “Why don't we stay like this for a while, before we head back?”

Gohan nodded happily in response, and curled up with his father on his chest. 
“I'd be happy to spend day after day with you, father.”
Goku looked curiously at his son, 
“It seems you're in a much better mood.”
Gohan giggled and pecked him on the cheek, 
“It's because I know how much I love you now!”