Shohei Sendo’s father’s remarriage leads to mc having a step sister, Rino Mizusawa. Rino’s appearance is that of a typical GAL, with blonde hair, piercings, and a mini skirt. Shohei and Rino, with their different interests and communication styles, would not have normally been friends, but they now live under one roof as siblings. Rino, who is not ashamed of wearing only a bath towel in front of Shohei, becomes friendly with him as siblings. Shohei, who thought that his sister was shy and spoiled, finds living with a GAL to be difficult. However, he discovers that Rino shares his otaku interests and their communication improves. One day, they find themselves alone in the bathroom. Being in close quarters, Rino’s body appears attractive to Shohei, and he kisses her lips.