Seijuu Ane to Junjou Kanojo ga H ni Ore Soudatsu Sen

The protagonist confesses his feelings to his childhood friend, a hot-headed blonde, and gets a positive response, leading to his first sexual encounter with her!
It's all smooth sailing! Feeling unstoppable, the protagonist rushes into his house and begs his strong-willed, black-haired sister, who treats him like a sex toy, to end their relationship, but she ends up straddling him right there!
He thinks he has to somehow end his relationship with his sister, but he just can't seem to win against her.
Then his childhood friend, ready to fight, barges into his house! And of course, his sister fights back!
As they physically struggle, things slowly take an erotic turn...
What will be the fate of the protagonist caught between the two?

[From Gyutto]