Hirotoshi

Hirotoshi is Mimori's older step-brother. He wants to get the "real" Mimori back.

Appearance
Hirotoshi has long, black hair that he usually wears in a ponytail. His face is round and his chin as well as upper neck are covered with a stubbly beard. As for clothes, he usually wears a plain white t-shirt and shorts. When leaving the house, he wears a dark   jacket over his t-shirt and puts on jeans.

Personality
While Hirotoshi acts stubborn around his father and makes no efforts to look for a job (despite his age and his father's new relationship), he is immediately enamored with Mimori and does whatever he can to make her just a little bit happier, for example offering to teach her his "special skill" or buying her new shoes without laces so she won't have to trip because of her shoelaces getting undone. For her sake, he's fine with coming across as a stalker.

Background
Hirotoshi lives with his father and usually spends his time playing video games and reading manga. His most prized possesssion is his collection of "little sister books", manga that include or revolve around the trope of the "imouto", the perfect little sister.

His everyday life is interrupted one year before the events of the current arc by the arrival of his father's new fiancée and her daughter, Mimori. Hirotoshi is overjoyed by this because he always wished for a little sister. He starts watching her from his room and pays a lot of attention to her.

While their parents are away on a honeymoon trip, Hirotoshi attends the parents' day at Mimori's school instead. There, he witnesses Mimori's death: she falls down - presumably from the school rooftop - and hits the ground below. When Hirotoshi runs outside to check on her, though, Mimori isn't dead but rather alive and more cheerful than ever, even calling Hirotoshi "Onii-chan". This sudden shft in personality makes him wonder if she's the "real" Mimori.

He continues to follow her as a full year passes. One day, he loses sight of her and finds her in an alleyway with a sword in her chest. He "rescues" her and almost gets run over by a truck, but then wakes up in his room again. When he looks over to Mimori, he notices that the wound from the sword has completely disappeared. Now he's certain that this Mimori isn't the real one and decides to get her back.