Chisao is a skilled girl who works in the general affairs department. But her only problem is Yoomi, a junior employee who recently arrived. The two, who often played together when they were young, ended up working at the same company, but now they just treat each other as colleagues. Yoomi has no trace of the cute face she once had, and her attitude is curt. It's more convenient now to have a relationship where we're not childhood friends. It was supposed to be...but at his welcome party, my past was revealed! ? Chihaya takes Yoomi out to quiet her down, but her heart can't stop pounding when he whispers her old name, "Chi-chan"! ? Furthermore, Yoomi laughs like the spoiled child he used to be when he hugs him and says, "I'll keep it a secret from everyone, so let me spoil you.'' After a chance reunion, her feelings for her beloved older sister continue unabated.