Ore no Otouto no Honjitsu no Onedari

"I want to have sex with you, nii-chan."
That one sentence from my younger brother made my - Ichinose Chihiro's - life do a complete 180.

Chikage and I are brothers that get along well.
It's been a few years since I started to live together in Tokyo with my responsible younger brother, who is also a mangaka.
Is this a punishment to me for relaxing into this comfortable lifestyle?!
While I'm stupefied by the sudden declaration of "wanting to have sex," my younger brother approaches closer.
Even if he needs it as a reference for his work, w-we shouldn't do such things-!!
But if it's my cute little brother that's pleading me so desperately, I might... just give in... maybe...
What should I do?!

This is a perverted scramble of a battle under one roof!