Cleavage Episode 1: Erika

Story

The protagonist 'Yuto Todo' is an ordinary student attending a certain academy. His father is promoted and transferred, and Yuto sees him off at the airport. From there a life of just the two siblings begins. In truth, his older sister and Yuto are not blood-related. Into the home of Yuto, who was raised without a mother, came a new mother and older sister (Erika). The mother was very kind, but she collapsed and passed away just like that... such was their relationship. On the way home, the two are talking in a nearly packed train when the train sways, and losing his balance he staggers and presses up against her. Like a couple who've just started dating, they act awkwardly, cheeks flushed. Erika, seeing Yuto still gazing at old photos murmuring 'Mom, Mom,' picks fights with him at every turn and tries to keep him under her thumb. At first bewildered by her attitude, Yuto—but over time he realizes his feelings are gradually changing from avoidance to something close to love. And Erika too stops hiding the fact that she came as Yuto's older sister and as a substitute mother, and comes to treat him as one woman. When their academy's music teacher, Sayaka Ichinose, happens to learn of the relationship unbefitting siblings between Yuto and Erika, she uses it as leverage...