Rouge wanted to enjoy gaining weight.
She didn’t want to plump up to immobility immediately. The journey is as important as the destination, and all that jazz.
So, she limited stuffing sessions to twice a month, and upticked her daily calorie count. Two days of nothing but steak, pasta with thick cheese sauce, and rich, delectable chocolate topped off with wine.
It happened slowly, but she adored waking up after days of indulgence and finding her weight creeping up, bit by bit. By six months, she’d put on twenty pounds, and it showed on her formerly lithe frame. 
Shadow noticed, of course, but as long as she could still go on missions, he couldn’t care less. 
After six months, she wanted more, and moved up to one a week. A good portion generous paycheck went to the finest foods money could buy, and her body started growing more than ever.
By a year, she decided that active missions weren’t for her anymore. She could live four lifetimes on the jewels in her collection, and devoted her time to eating. Rich breakfasts of half a dozen eggs and bacon, lunches and dinners of every kind. Her stomach blossomed, and when she couldn’t see the scale over it, she celebrated with a feast that packed on nearly ten pounds.
Her arms thickened, and she couldn’t walk without her thighs rubbing. 
After a year and a half, she couldn’t fly anymore, but who needed that, when she had herself, and all the delicious riches money could buy?
She bought a tube-feeding machine at a year and a half, and it pushed her further. Her belly was nearly as big as she was tall, and her cheeks were perpetually full and flushed. Her breasts were as large as her head, and her entire body was pillowy, lush fat on every inch of her.
She hired a maid soon after purchasing the tube-feeder, one that she required to not only cater to her every whim, but to tell her how beautiful she was, how she would get fatter every day. The ad had mentioned this would be part of the job, and for the maid, a cat with silky black fur, it was a dream come true to feed and worship a woman like Rouge.
By two years, she rarely needed to leave her bed, and nearly every calorie consumed became lush, soft fat that the maid caressed and adored, showering with kisses in between pressing rich sweets into her mistress’s mouth. 
It was a good, good life.