She could possibly have macromastia then if one boob is that much bigger then the other, not every case results in immense cup sizes. The fact she is as skinny as ever, yet her boobs are bigger then ever is a tell; plus her disproportionate boobs are a dead giveaway. Technically your chest only has to be 3% of your body weight to have it, and Hitomi looks like she qualifiys.
I'd say she definitely qualifies. When I lost a bunch of weight, the "girls" remained. That is a giveaway that the growth is from something other than fat! It's also normal to have one boob a bit smaller than the other. Other times, they might grow in different directions (one might hand lower, while the other might project more to the side). All part of the beauty of natural breasts
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