Kedamono (Kazoku) tachi no Sumu Ie de

♡ A lewd, lustful nun older sister & a mean, vulgar bunny girl older sister ♡
You’re a pure, petite boy captured by naughty, busty older sisters, forced to do nothing but be made to climax by the older sisters you love so much…!

In this world, there exist SR girls. Special and Rare girls—meaning extremely rare. SR girls... they are girls who are the only ones of their kind in the entire world. Due to their uniqueness, the SR girls cannot even understand who or what they are themselves. They feel confused about themselves. Their identities waver. To resolve these things, they needed to "grow." And the ones who could help them grow weren’t the adults around them. No, it was a boy—the only one of his kind in the world.

The protagonist, Takatoo Mitsuki, was working hard every day at his part-time job. Then, one day, he was suddenly taken by a suspicious person to a strange place and brought to "Saint Marianne Girls' Academy." There, the protagonist was told a shocking truth. He, too, was an SR.

The protagonist protested: "But I have my part-time job"
To this, the academy’s headmistress replied firmly: "The work you’re truly meant to do isn’t some part-time job. Your most important job, the one where you can shine the brightest, is to help the SR girls grow."
And so, a new job—"helping the SR girls grow"—began.

"We're gonna found a band for sure, I promise!"

With this promise, the protagonist had parted with a boy from his childhood. But already 10 years later, it was time to move again. Summer passes and by late September, the protagonist had already returned back to his hometown again, due to his father's job situation.
He wonders if that friend from back then still remembers their promise...

Being torn on whether to be hopeful or to give up, the protagonist introduces himself to the class as the new transfer student, is met with baffled eyes and gets hugged by a girl unfamiliar to him.

Could it be? That's the boy from his childhood! The protagonist is also baffled by how much his appearance and looks had changed. Does he still remember the promise they had made when they were children?

The protagonist looks at him sincerely and asks him for his support if he still wants to continue making music.

And from this day on, he and three other boys begin forming a band, whose goal it is to perform a gig on the school cultural festival's stage.

While as pursue that goal, their bonds deepen and these boys don't realize they've already awoken to a new pastime of their's.