Long black hair flat-chested tsundere younger sister Miu. Because of bad studyphobia, the grade of mathematics is descending rapidly. Kanata to pocket money improvement, a tutorial role is given by mother. However, the younger sister of puberty rejects becoming only two people with the elder brother. After both compromise, younger sisters friend Riko is adds, holding the study meeting by three people. Brown hair twintail and huge breasts Riko. Additionally, it is lovely. Such Riko, goodwill is sent to good Kanata. A devil smile is floated, Riko that always sticks to the body of Kanata while studying. Younger sister who gives a glare to elder brother of lovestruck condition. When suddenly noticing, both have drawn near to Kanata!? With a tsundere younger sister of puberty, huge breasts slightly gal-like friend of younger sister. Which is chosen in case of you?