Mitsui Hana

The protagonist's younger sister.

With the birth of their long-awaited daughter, the sibling parents' flower garden was in full bloom, and they elaborately named her after it. However, it was only after the birth certificate was submitted that they realized that the phonetic pronunciation of the name was "Baka", as in "Stupid".

She's innocent and very positive, but perhaps because of her name, she's also an idiot who doesn't think about anything, prancing around completely naked at home with no sense of shame in her bones. She has no sexual knowledge whatsoever, but gradually learns to take pleasure in the act of "studying" with her older brother, the protagonist.

She is glad that there is something that she can do, even though she is an idiot, and begins to actively seek out the deeds.

"Wow! Onii-chan can produce milk from his penis!"