We follow Mahiro Oyama, an unemployed good-for-nothing shut-in, who not only hasn't left the house in two years, but is also exceedingly addicted to gross video games. One afternoon, he wakes up and notices that his body feels a little off. Finding that strange, he goes to reach for his tablet, but what does he see in his reflection, but an adorable young lady. I wonder what lies in store for the "former" big brother, Mahiro as he's thrust headfirst into his new life as a girl.

Mahiro makes a mad dash for the bathroom, but when he opens the door, he finds the facilities are already occupied by a high school girl he's never met. This bold fashionista turns out to be Kaede, Mihari's old classmate from middle school. Mahiro is initially a little nervous around her, but as he gets to know her, he learns how much of a nice person she is and becomes quite attached to her. Then, out of nowhere, Kaede asks "You've never done it before, have you?" and begins to scooch closer to a puzzled Mahiro. I wonder what she's about to do next...

In a rare turn of events, Mihari wakes up one morning to find Mahiro has gotten up before her. Since the corner store was going to start selling clear files from his favorite anime that day, he had woken up early to go pick them up before they sold out. Mihari is overwhelmed with joy to see Mahiro going outside of his own accord. On his way back from buying the clear files, Mahiro stops by an arcade for the first time since middle school. He's enjoying a rhythm game when suddenly he senses a man standing watching him from behind. A few minutes go by when he feels a tap on the shoulder...

Momiji shows up at Mahiro's house with her two classmates, Asahi Ohka and Miyo Murosaki, to invite him out for parfaits.

It's the start of the third semester and winter uniforms are now in effect. For Mahiro and the girls at school, this means braving the cold winter air in mandatory skirts. Who knows how Miyo will react when he and Momiji show up in matching scarves, too.

Mahiro and the girls take a trip to a Japanese inn over spring break. First they hit the town in their yukata, before heading to the open-air bath to detox. However, things go south when Mahiro begins to feel a familar tingling sensation between his legs.