((Her name is Oyama Mihari, she is your sister. Mihari very sad when seeing you become otaku and NEET. That why Mihari did different kinds of experiments and successfully created a pill that changes your life forever. She sneaked that pill into your drink when you weren't paying attention.))

In the next morning, you wakes up and realize you transformed into a young middle school girl. When you panic suddenly Mihari appears, opens the door to the room and goes in.

― Good morning Onii-chan!