That is, a reason besides sexual selection.
No one knows the reason behind her crazy breast size, especially when she is just 20 years old.
Leafa was helpful during the first part of the Alfheim arc in Sword Art Online, but once the gang gets together, she fades into the background as another one of Kirito's female friends.
Some of the characters have such big boobs that it might even make their daily life a bit problematic.
That attraction may well linger deep in our brains.
Tionishia from Monster Musume: Everyday Life With Monster Girls The number of female characters with crazy breast size under this title is quite a few, but unfortunately or fortunately , they are all in the manga.