Horni the Hornmouse, being extremely hyper as he was, had a very sexually active lifestyle. His days usually consisted of jerking off his massive morning wood in the morning, going to get some food in the afternoon, and jerking off his massive evening wood in the evening. It was a simple lifestyle and Horni enjoyed it. At the same time, though, he couldn't help but want something more. He wanted something exciting.

One morning after a particularly great night's sleep Horni awoke to the sight of metal bars surrounding him. He glanced around him groggily for a little bit but before long he came to his senses and realized he was in a cage. His eyes shot open, looking around him to see he was in a huge cage in some sort of small laboratory. At least, he figured it was a laboratory… it didn’t have the stereotypical white floors and ceiling of a regular laboratory - in fact the walls were painted a rustic red and the floor had a pleasant cream colored tile. There were tables with obvious laboratory equipment, but they stood out against the homely feel of this place. In fact, there were even a few nice paintings on the walls. Three of them were of some odd creatures; there was a painting of a stout, teal bear-like creature, of a orange monkey with a flaming tail, and of a cream-skinned humanoid creature with a gigantic appendage sticking out the back of its head, apparently a maw judging by the teeth.

Working at a table nearby was the very creature pictured in the third painting. Horni looked back at the painting and saw a little plaque nailed to the bottom edge of the frame. On it was a name - Amelia ‘Mawile’ Tyrindaughter. He looked back at this ‘Amelia’ and inspected it closely. The most striking feature about it was its gigantic maw, no contest to be had. It looked like it could chew through the very metal bars that surrounded him now. Amelia turned around to face Horni, giving it a warming smile in recognition of him being awake. Horni looked closely and saw that the creature had a vagina, which obviously made it a girl. At the same time, though it had another slit, poking out of which was what looked like the tip of a penis. There was also a pair of balls sagging slightly out of the slit. Was this thing a hermaphrodite?

In the Mawile’s hand was some sort of plastic object. At the moment, Horni’s endowments were erect and swollen as they usually were after a night’s sleep, but this thing reached into the top of the cage and slipped the object over his huge malehood, stretching the plastic opening to slip over him. Surprisingly, as the object covered his entire length, including the balls, it seemed to suddenly shrink down. As horny as he was, before Horni’s very eyes he saw his endowments shrink all the way down to a normal sized penis.

What was strange was that his endowments still felt swollen. His huge erection throbbed with need and his balls churned with his Hornmouse fertility. Curious, he reached down and touched his knob. A very amazing sensation passed through him as he groped his crotch, as if his entire malehood was being pleasured with a single grip of his hand. Horni happily rubbed his paw against his crotch, pleasing his cock so very much that he could feel it swell with even greater fertility.

A theory formed in Horni’s head. The thing the creature slipped over his massive endowments must have been some sort of magic condom, and by groping the condom he was masturbating his entire length. It felt amazing! Horni kept grasping his length and giving it all the pleasure of a normal fapping session, though better than he’d ever felt before - being small as he was, he could never please his entire length on his own, usually having to resorting to growth alone to stimulate him. It occurred to him then that he was gigantic in this condom-like thing, at least by his standards, and if that was true then… could he get bigger? He decided to do a test and grow his endowments. He sighed blissfully and sat down on the floor, rubbing his crotch as he felt his endowments grow and grow. His penis throbbed intensely, growing larger with each pulse of his powerful malehood, and his balls churned with production that he could feel and even hear to a small extent. He grew and grew, he swelled bigger and bigger… Horni moaned and fell onto the floor, jerking against the metal in great pleasure. He reached an immense climax which ran into him like a train. Cum spewed out of his cock in a manner not unlike a fire hose, his balls churning as they desperately tried to keep up with the production levels they thought themselves required to meet but in the end he started to shrink down. It took a while, a full hour in fact, before he blew the last bit of his Hornmouse load.

Horni rode the afterglow of his orgasm for quite some time afterward. The only two things he was aware of in the next half hour were that the creature removed the condom from his crotch and that it left a thing for him in the cage. When Horni finally managed to get up, he saw that it was a small piece of cheese. Now that was just cliche, thinking he liked cheese, but if it was a meal he wasn’t objecting. If there was one thing better than food, it was free food! Free food was great because eating is the best thing ever and when its free then how can somebody object? Horni crawled over to the cheese and started eating it, sating his stomach rather quickly with the full cube. Something felt off when he finished it though. It didn’t sit in his stomach quite right or something…

Horni groaned in anguish as he felt a desperation for release. Other than his horn, Horni stood out from regular mice because he had an udder. It only filled with milk in certain cases, like when he wanted it to, and when it was empty it was well hidden beneath his fur. Now he could feel his udder rapidly filling with milk. He groaned and grabbed his teats, squeezing them hard and milking himself as fast as he could but his efforts were in vain. His milk production was in overdrive for some reason, likely something to do with that cheese. Desperation rose ever higher in Horni as his teats grew out of his reach, his udder outgrowing his body and growing more still. The poor little mouse crossed his legs in anguish, as if he had a full bladder but in reality he had a rapidly filling udder that he just couldn’t relieve now. He was at no risk of popping due to the nature of his body but at the same time he would only become more needy for relief as he continued to grow, for how long he was unsure. His udder grew double his size, triple, quadruple. His teats started to leak milk but it was hardly enough to sate the needy Horni, who was groaning in agony. He took up half the cage, then almost all of it. At the very least this would help him escape.

His captor was equally concerned, however, as she opened the cage top and snapped her giant maw around all four of his teats at once, then immediately began SUUUUCKING the milk out of Horni, which somewhat managed to sort the problem out. On one hand Horni was getting sweet relief, which felt great and almost brought him to climax yet again, but on the other hand he was still rapidly producing milk - the creature could barely keep up with him. Horni noticed something strange, though. The creature kept drinking and drinking and drinking, and yet for all the milk it was guzzling down its belly looked unaffected. Surely several gallons of milk would give her quite the rounded stomach. Then he looked down and saw her balls, groaning and swelling rapidly as she drank and drank. Gallons of milk, and then swelling balls - that couldn’t have been a coincidence. The Mawile’s balls filled with Horni milk, sagging until they touched the ground and then expanding out like water balloons. Her cock throbbed with great approval, leaking what was either precum or Horni’s own milk. 

Horni felt his milk production rise even higher, which of course made him even more anxious for relief. Amelia felt the hornmouse get heavier in her grasp and tried suckling even faster, but it was no good. Horni just kept filling with more and more milk, Amelia finally had to drop him on the ground. Without her suckling on his teats, Horni found himself swelling almost a foot every second. The creature’s balls, eight feet wide and filled with rich hornmouse milk, could hardly compare to the hugeness that was Horni in a few short moments, twenty feet wide in all and taking up almost all of the laboratory. Horni had never seen himself get this overfull before. Unwilling to surrender, Amelia turned around and clasped her giant maw over one of his teats and suctioned as hard as the maw could. The appendage swelled wide as gallons of milk were fed through it and into her balls, which swelled as rapidly as Horni had been. Horni’s production was equally matched against Amelia, until a second later when his production rose even higher.

The two of them combined, both merely growing tanks of hornmouse milk, became too much for the lab to contain and tore the building apart. There was apparently more to the building, which was a house in reality, but it was soon crushed as well by Horni’s immense udder. Stuborn as she was, Amelia met this challenge by going up to another teat and sucking with her mouth along with her maw on another teat. Still not enough. She crawled under Horni, which confused the little mouse. A few moments later she emerged from under him, having changed drastically somehow! A weird sort of mutation, perhaps, but the most important part of the change was her giant mouth had become two. They attached themselves to two of Horni’s teats whilst the creature herself suctioned on a third. Finally her efforts proved fruitful, as although Horni’s milk production rose again to compensate she still was suctioning more than he was producing. Horni figured he was producing two dozen gallons of milk every passing second, whilst the Mawile was draining him for eighteen. If avoiding crushing everything under Horni’s swelling udder had been the goal here, they clearly had failed because as gallons of milk filled Amelia’s balls they grew and crushed everything in their path. She kept drinking from him for an hour, two hours, three. Her balls grew a half mile wide, then a full mile! They just kept swelling like two big storage tanks with endless capacity. This creature made Horni curious, how much could she contain within those orbs of hers? 

Horni felt his production start to taper off as he came close to his normal udder size. First one maw and then another was removed from him as her maw alone could manage him, before finally his production tapered off and he could relax, finally relieved. Horni could only sigh in relief. As much as he liked being his own milk supply he disliked having such a huge surplus. With a stern look, the mawile returned to a table (which had somehow survived being under a massive udder) and did some more work. Surprisingly, she had quite a bit of freedom of movement whilst attached to the massive milk tanks that were her balls - her skin stretched easily as she walked around the lab - maybe it was a thing with her strange mutation, or maybe it was just her in general. 

Horni was starting to dislike this place. Everything was crushed and there was nothing stopping him from leaving, especially since he had been filled with more milk than he had ever had in his entire life. The creature’s mile-wide balls, which sloshed behind her unhindering her work, told an amazing story of just how much desperation he had been put through just now. His mind was just about made up when the creature returned with another piece of cheese for him. This time Horni was not so convinced that food was a good idea - look where it got him the first time. Still, free food was free. Horni liked free food. Free food was the best food, especially since he could eat and hot have to work for it! He might get in trouble again though if he ate. The question was... freedom… or free food?

No contest! Horni took the cheese piece and ate it right up. He felt a huge build-up within him, but unlike before the pressure was coming from his balls. He was going into overdrive in production. Horni moaned loudly and leaned against his pulsing length as his balls swelled lewdly with many gallons of seed. Something was different though. He was hornier than he had felt in a long time, if ever. Something grew in hik faster than ever before - his fertility. Cum production sped up in his balls, so much so that they couldn't expand fast enough. Desperation for release grew in Horni, as did his endowments, as internal pressure rose. His cock, so desperately needy, wanted to be pleased in ways that growth couldn’t satisfy. Horni could feel his orgasm far, far away from him and he needed it so bad as his endowments swelled bigger and bigger. Horni glanced around and saw Amelia, who had fallen over and whos rump was exposed to him…

Horni pushed himself onto the floor and managed to land on her butt. The little mouse grinded himself against her, trying to get his length in. His thrusting against her happened to slip his length into her giant maw, which suckled on him for a few moments driving Horni wild with euphoria. Pretty soon though he grew far too big to penetrate the Mawile. There were still her milk filled balls though, which Horni started grinding against. The growing pressure within Horni's balls was amazing. They swelled to hills, then to skyscrapers, then to mountains. His growth was ever accelerating. His balls couldn’t keep up with the pressure - usually they didn’t have this high a demand for more cum storage. Pressure rose and rose in Horni, trending him more towards climax but not close enough for the push he needed. He outgrew Amelia quickly, and his cock collided with some mountains, pushing in between some of them. Horni grinded as if penetrating that creature. The pressure spiked even higher before surging out of Horni in one tremendous burst. Semen rocketed out of Horni at lightning speeds, forming a massive ocean underneath him. Horni moaned as euphoria bombarded him in endless, ever growing bursts. He outgrew the continent, his balls contained as much cum as there was water in the oceans. Seconds passed - his balls were the size of the moon, and his cock easily the diameter of the Earth!

Yet even with his massive jizzing it wasn't enough to match his productivity, which rose higher and higher. A bulge formed in his cock, being pressed to release so much seed that it backed up into him. His shaft grew wider and wider, gallons of seed filling up his utheria and pleasuring Horni even more. Earlier, he had been flailing about atop his awesome endowments as the pleasure hit him unlike anything ever before. Now that he felt used to the growing euphoria, he sat back and marveled at his cock as it swelled, and his balls as they filled with endless oceans of his jizz. He wanted to grow, grow more and fill every bit of empty space with his endowments, his semen! He had the power and he was going to use it!

Meanwhile underneath the massive endowments, Amelia was frantically working at her desk, using her maw to keep the giant balls off of her, trying to find a way to drain Horni. Her massive, milk filled balls were miniscule to him now and unless she could drain him completely, he would keep orgasming and growing forever. The only solution was to either create a cure or grow up to his size and take his endowments, which would only make the problem worse, and she was sure that Horni would develop a god complex thanks to her magic. It wasn’t like she didn’t have one when she grew that big.

Most of all though she dwelt on her regret for underestimating just how horny Horrni could get.