A public library in the center of Mitakihara City, one of the biggest in fact. Shelves filled to the brim with books, magazines and other various works of literature, sorted by author, title, content and even keywords. Among these shelves, a creature lurked, it's looks much akin to a cat or a squirrel. It was our titular Kyubey, of course.
He decided to research the matter more thoroughly, as it was crucially important not to get it wrong. As awkward as it was at the start, when he only vaguely imagined what a "bigger magical girl" would look like, he finally narrowed down the desired outcome to a few different viable processes. In alphabetical order, they were called: impregnation, gaining weight and natural growth. There were more, but these seemed the most commonplace, according to the amount of literature on these subjects. Considering each of these, natural growth could be ruled out. It took too long, and he also read that females grow more slowly than males. Also, there was no record of a female achieving the volume he required with shear natural body growth.
Impregnation seemed to be the result of human procreation. The child grows inside the female and this results in the belly swelling and stretching. The different balance in hormones also causes the female's breasts to increase in volume and weight, as they prepare to produce milk for the baby for when it is born. When reading books such as First-time mommies,Carrying life and My tummy feels funny, he noted that pregnancies usually end in increased weight for the female, as her appetite is increased, which can safely feed into the second possible method.
Weight gain or gaining weight is much different to the former, as it seems to carry only a negative connotation, with many health disadvantages, such as increased blood pressure, less agility and body fitness, depression and in extreme cases death. These "side effects" can be safely disregarded, magical girls aren't supposed to have long lifespans anyways. Weight gain is achieved through continuous intake of foods rich in fat and sugar. What seems to be key is to never cease on the intake for too long, and also to increase food intake exponentially. Not much is written from here on, it only says that "extremes kill". Well, what's the worst that can happen?
He decided to combine the two. Pregnancy should be achieved artificially, and in such a way that it would show results immediately and produce no offspring. Besides, humans shouldn't suffer unnecessarily. Specifics will be determined later, but first, he needs a test subject. That will be...