No way! Cruel Mai! You can't say such a thing to your dear sister.

Once Kozue said that she didn't mind if Mai made a mess of the book i immediately thought there was a yuri manga in the bag ( ͡° ͜ʖ ͡°)

The mangaka forgot about the "But She Doesn't Mind" part of the story

inb4 sis gets her a Onee x Imouto manga

A cute imouto's ultimate weapon is dreadful. "If you do X thing, I'll hate you"

I mean, she is being targeted...

@Dreecko If I had to guess, the same thing she's been doing since the beginning. Sleeping in her sister's bed and getting off on the scent of her pillows.

Okay I still curoius, what was she doing before she hides under the bed?

*POMF* Wah! Onee chan, what are we going to do under the bed?

I bet it was written by their mom

If the manga was Onee x Imouto instead of Senpai x Kouhai I bet she would approve.