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.

[Translated from the official website]