Fantendo no Imouto, or simply Fantendo Imouto, is a community project, and somewhat of a parody of the visual novel Imouto Senbatsu☆Sousenkyo.
On the day of Victor's imouto Victoria's birthday (which is Halloween, because in his family every day is Halloween), his father returns after a long absence, and reveals both that he is dying, and that Victor has 364 other imoutos. The Halloween Spirit needs to choose his successor from his children before he dies, and wants Victor to talk to each of his imoutos and find who is most worthy and capable of becoming a spirit.
Victor and Victoria transfer to a new school, Fantengoku High, where Victor discovers that not only is the only male student, but all of the other students are Victor's imoutos.
At the end of the day, Victor goes to the male dormitory to find his room and is surprised to see one other student, Pablo; she was also his imouto, but through an error in the school's database had been assigned the male uniform and a room in the male dormitory.