The heroine, Manaka, loves Haruaki-kun, and one day he asks her to go out with him.
One day, he asks her to go out with him. However, Haruaki has a propensity that he can't tell anyone about.
However, Haruaki has a proclivity that he can't tell anyone about, and that is that he likes little sisters(imouto) who look like the characters in slice of life anime.
But actually, Manaka is the same way, and says, "I wanted a kind older onii-chan(big bro) too.
So Manaka proposed that she and Haruaki go out as lovers and siblings.
Haruaki is dreamy at Manaka's unexpected proposal, but then Aika's abnormal obsession with her "onii-chan" begins.
Manaka's obsession with her onii-chan begins.

[From itch.io]