On a cold winter's night, a man finds two girls—Saori and Shiori Mizuki—seemingly lost in front of his apartment. Since then, the twins have gradually become attached to him, with one staying at his place while the other is at school. However, the sisters' relationship with him is not merely that of a babysitter and child because sometimes more mature events occur. [Written by MAL Rewrite]

A series of animated promotions for tower defense mobile game Arknights.