Onii-chan Is Done For! Official Anthology Comic - Vol. 3 Ch. 36 - Mahiro and Schrödinger's Nayuta

[Taper]

Really, there's still an outside possibility that Nayutan is an adult woman that's also been aged down, but it's pretty unlikely.

 

[eirianrobotto]

how did the most sane people recommend Onimai to me?

 

[Taper]

I still don't understand what that picture of Earth meant (page 7). Some sort of pun?

Oh, actually I know this from Seitokai Yakuindomo! The pronunciation "chikyuu" when spelled 地球 means "Earth" or "the globe", but spelled 恥丘 it means "mons pubis". So it's a pun on the part of Nayutan that Mahiro accidentally saw.