Mei’s breasts are the largest of the cast, and all of New Primrose simply because she is!

Mei’s growth is based solely on her genetics, as opposed to some random factor, as she comes from a long line of women with rather mountainous mammaries, with her mother, aunts, grandmother, and great grandmother all possessing the same growth. As all growths are genetic, it only makes sense that it’d be passed down to her!

I should also mention her growth is considered bodily by design, as it awoke during her late adolescence as she was finishing up high school, with her chest coming in and never stopping as college came and went (you should have seen her at her college graduation, she took up the whole stage!)

On the topic of her size specifically, it’s a mix of how her growth operates and the fact that some Hypers tend to grow larger than most. When her growth began, it gradually increased without stopping until she reached the size she is today, being the current largest Hyper. At the same time, it’s something of an uncommon occurrence for Hypers to grow far larger than most would, reaching the largest of sizes on the known scale, and the only two folks to do that currently have been Mei and Renée.

Talk about breaking the status quo! If anything, Mei practically flattened it!