Während er über Pläne für das Schulfest spricht, behauptet ein kleines Mädchen, Pontas kleine Schwester Emi zu sein.
It was a wonderful morning the Yokodera and Tsukiko went to school together while discussing their plans later than day for the school festival then suddenly a pink-haired little girl showed up, then it accrued that she was Ponta's little sister named Emi. Emi kept calling Yokodera onii-san (big brother) and seemed very friendly with him but at the same time Tsukiko seemed not to like Emi very much and had a feeling that she is a evil-plotted person,then she said that Yokodera should take Emi for a tour of their school and would wait for him afterward for their practices.Emi learned that Yokodera is a well-known "pervert" is his school so Emi took out a Cat-statue-figure like the one found in the storehouse of Tsukiko's house and wished Yokodera would be a "cool" guy in his school. Weird thing happened, the school suddenly having Roman ancient architecture like the Colloseum, every girls in the school called Yokodera as prince and the school swimsuit as the uniform in the school. Tsukiko showed disbelieve when Yokodera told her it is not his doings. Tsukushi suggested to go to Yokodera's house after asked Yokodera to send his 'yonger brother' a message. After seeing a photo taken out by Tsukushi when she is visiting Yokodera, he found something weird about the girl, Emi, because the name 'Emi' so happened to be Ponta's rabbit's name.
Yôto doit soudain gérer une nouvelle prétendante : Emi, la petite sœur de son ami Ponta… Une jeune fille très… entière !
横寺の顔面に足蹴りを喰らわせて、謎の美少女エミが現れた。"ポン太の妹"であるエミは、100％完璧な笑顔で横寺を籠絡。横寺の案内で高校を見学をすることになった。しかしエミが猫神のぬいぐるみに願ったことで、世界は変容してゆく。
要注意人物"変態王子"は、全校女子憧れの的の格好いい"王子"に。女子の制服はスクール水着に――。水着女子にかこまれて、横寺は学園生活を満喫するのだが……。はたしてエミの真意とは!?
요코데라를 오빠라고 부르며 나타난 귀국소녀 에미. 그녀의 완벽한 미소에 요코데라는 혼이 빠지고, 츠키코는 그런 에미가 왠지 맘에 들지 않았다. 고등학교를 구경하고 싶다는 에미의 부탁에 요코데라는 교정으로 향하는데...
Emi, una chica que apareció llamando a Yokodera 'oppa' (hermano mayor) mientras regresaba a casa. El alma de Yokodera se escapó ante su perfecta sonrisa, y Tsukiko de alguna manera no le agradó esa Emi. Ante la solicitud de Emi de querer ver la escuela secundaria, Yokodera se dirige a la correccional...
