Keita Suminoe (住之江 圭太 Suminoe Keita?)
Voiced by: Ken Takeuchi
Keita Suminoe is the main protagonist of the series. Blended into a step-family when, at childhood, his father remarries (his birth mother passed away when he was young), he comes into the acquisition of a stepmother and older stepsisters, Ako and Riko; an arrangement he welcomes. A 15-year-old,[3] third-year middle school student, and under the now persistent debauchery of his siblings, Keita finds it increasingly difficult to retain his modest, dignified morals; especially when his parents encourage him to indulge! A former track and field member, Keita is athletic more than he is academic; however he strives to and eventually is accepted to his stepsisters' high school. He is a first-year high school student in the same class as Miharu, with Yuzuki Kiryu as their homeroom teacher.
Ako Suminoe (住之江 あこ Suminoe Ako?)
Voiced by: Ayana Taketatsu
Bright and cheery, Ako Suminoe is a 16-year-old,[4] first-year high school student who is one of two stepsisters to Keita, twin sister to Riko. The more intellectual of the pair, Ako is educated, maternal, responsible, President of the student council, skilled at cooking, homemaking, and endeavors to maintain a prim and proper demeanor. In spite of this imposing façade however, she is outwardly emotional, childish, whiny, reluctant, easily embarrassed and perverse; her most well-known open secret. Having grown up with Keita since toddlerhood, Ako is altruistic and, of course, in love with him.
Riko Suminoe (住之江 りこ Suminoe Riko?)
Voiced by: Yuiko Tatsumi
Riko Suminoe is the second stepsister to Keita; a fellow 16-year-old,[4] first-year high school student. Though less accomplished than her counterpart, Riko is interpersonal, cunning, insightful, crafty, an active member of the disciplinary club, and boldly open about her personal life and sexuality; although she surprisingly cannot bring herself to kiss Keita in front of others. She is known however, to be soft-spoken, clumsy, temperamental and weaker to alcohol than her sister. Riko is most recognized for wearing an adhesive bandage on her left cheek, the purpose of which covers a scar she received from when Keita threw a toy at her during their childhood.[5] In a complimenting fashion, Riko is also ardently fond of her stepbrother and forever fighting with Ako over his affections.
Miharu Mikuni (三国 美春 Mikuni Miharu?)
Voiced by: Yoriko Nagata
Miharu Mikuni is a third-year middle school student. A fairly quiet and unknown character, she is brought into attention when she delivers Keita his entrance exam results; having passed, he joyfully befriends her. Unlike the other girls, Miharu is comparatively tacit, meek, intimidated and predisposed to anxiety; as such, she suffers from enuresis (this becomes a running gag in the series). Her relationship with Keita is mostly platonic; what feelings she does have for him are generally overshadowed by the images she has of him and his stepsisters. She sometimes fantasizes about Keita making non-consensual advances against her, but doesn't seem to be seriously interested in a romantic relationship with him. Of the entire cast, Miharu is the only bespectacled character.
Mikazuki Kiryū (桐生 三日月 Kiryū Mikazuki?)
Voiced by: Asuka Ōgame
Peppy and outgoing, Mikazuki Kiryu is a second-year middle school student and younger sister of Yuzuki Kiryu. In spite of her age, she is far more mature of the two, and tends to keep the most level head when her sister is losing hers. An underclassman to the rest of the cast, Mikazuki looks up to everyone, especially Keita, who she fashionably has a crush on. However, she seems to be just as interested in amusing herself by watching the antics and reactions of others than actually winning him over. Mikazuki lives with her parents and is the shortest character of the entire cast.
Yūzuki Kiryū (桐生 夕月 Kiryū Yūzuki?)
Voiced by: Asami Imai
Yuzuki Kiryu is a 23-year-old[6] homeroom and Japanese History teacher at fictional Gakushū Senior High, a recent hire, and is also the older sister of Mikazuki. While she constantly berates herself whenever she makes mistakes, she is a caring teacher who can lay down the law when she wants to but tends to get herself and others in trouble when she acts impulsively over perceived things without finding out the full story. One example is that she does not realize that Ako and Riko are Keita's stepsisters, not his biological sisters, until they tell her. Single, unmarried, independent, and noticeably eccentric, she is initially disgusted with Keita and his relationship with Ako and Riko, to the point of unduly crusading against it.[7] Ultimately, like the girls to come, and despite her age difference, she develops conflicting feelings for Keita herself. An obsessive fan of anime, manga and cosplay, Yuzuki's apartment spans a large collection of merchandise, books, games and posters; a particularly favored theme of hers being samurai.[8] She is so obsessed that her parents forced her to either get a place of her own (which she did) or give up her hobbies permanently. She often has to eat cheap ramen as she spends most of her money on so much paraphernalia to clutter her room and apartment that she can't invite anyone inside without them discovering her hobby. Much to her humiliation, Yuzuki is a virgin.[9]
