​When Kota's father gets remarried, Kota's first impression of his new step-sister Aika is that she is beautiful, but that image is shattered pretty quickly.
His new step-sister is a super sassy and foul-mouthed gal who behaves uncontrollably while their parents are away, making Kota's life a living nightmare.
However, their relationship begins to change when Aika gradually warms up to Kota's caring older-brother nature.
Aika Takamura
A girl who became Kota's sister. While having a very aggressive side toward men, and a kinder side to women, she also has a Mature side.
She starts off completely condescending to Kota, but a certain incident changes the way she interacts with him.
Kota Takamura
A young man who became Aika's older brother due to his father's remarriage. He has a somewhat logical personality, and he doesn't match the wavelength with the gal Aika and starts cursing each other from the first meeting.
After that, he becomes attracted to her through various events.
Yoshiyuki Takamura
Kota's father. He lost his wife and continued to live with Kota, but he met Misaki and decided to remarry.
Misaki Takamura
Aika’s mom. And after several fruitless relationships, she finally met Yoshiyuki, and reached her relationship goals.
