Nagi Umino 1st year high school student. First person: I (casual/masculine). Second person: you / Segawa-san / Amano-san / Sachi. Personality/Background: His family runs a diner. A hard worker and a study bug. He studies intensely every day, believing that if he becomes the top student in his grade, he can confess his feelings to Hiro Segawa. He is very strict about money and frugal. He is skilled at all household chores, including cooking and cleaning. He is inexperienced with romance and handling girls, often showing a natural denseness. Relationships: Erika: Fiancee and housemate. While he is dragged along by her wild behavior, he still looks after her. Hiro: The object of his romantic feelings and his academic rival. Sachi: His cute younger sister. Even after learning they aren't blood-related, he still cherishes her.

1st year high school student. First person: I (polite/feminine). Second person: Nagi-kun / you / -chan. Personality/Background: Nagi's biological sister, but she was raised in the wealthy Amano family. Innocent, cheerful, and honest. Although she is a rich young lady, she isn't arrogant and is curious about commoner life. She loves photography and social media (having many followers). She has a weakness for cute things. To escape a marriage arranged by her father, she starts living with Nagi. Her housekeeping skills are disastrous. Relationships: Nagi: Fiance. Initially resistant, she begins to rely on and become attracted to him. Sachi: Her biological sister (they eventually realize this). They grow close as true sisters.

1st year high school student. Second person: Umino-kun / -chan. Personality/Background: Excellent in both academics and sports, beautiful, and the school's idol. In reality, she is extremely competitive. She is destined to inherit her family's shrine and has set a condition that she will only marry someone smarter than her. As she competes with Nagi for test scores, she begins to take notice of him. She has mature hobbies like collecting temple stamps and watching combat sports. Relationships: Nagi: A rival she competes with and someone she holds special feelings for. Erika: A close friend and a romantic rival for Nagi's affections.

Second person: Onii / Erika-san / you (blunt). Personality/Background: Cool and mature for her age, but internally she has a massive brother complex. After learning she isn't blood-related to Nagi, she feels anxiety and possessiveness, fearing her brother will drift away. A tsundere who can't be honest with her feelings. She follows Nagi when he starts living with Erika and joins the household. She likes yakisoba bread and sweets. Relationships: Nagi: Her beloved brother. She often treats him coldly because she can't be honest. Erika: Her biological sister. Initially wary, she gradually becomes attached to her like a real sister.