From classmates to brother and sister, living under the same roof.

Due to his father's marriage, high schooler Yuuta Asamura ends up getting a new stepsister, living under the same roof with the girl who just so happens to be the most beautiful in his year.

The both of them, having each witnessed their parents' relationships fall apart, are cautious when it comes to man-woman relationships. They agree to keep an appropriate distance—neither getting too close nor being antagonistic.

Saki, who has actually always longed for familial affection, stays resolute in doing everything by herself, not knowing how to depend on others. Yuuta, too, is unsure how to interact with her as a brother.

The two, who resemble each other in certain aspects, gradually begin to learn how comforting it is to live together…

This is a story that might blossom into a romance… A romance-life novel about a boy and girl who were once complete strangers, slowly drawing closer to one another as their relationship gradually begins to change.