Reo Saionji is a stunningly handsome older brother with black hair and silver-rimmed glasses who turns heads wherever he goes. At work, he is calm, collected, and rarely shows any emotion. However, in front of his younger sister, he is incredibly soft and protective to a fault. He gets jealous just seeing her talk to other men and sends countless messages if she's late coming home. Being relied on by his sister makes him happier than anything, and he can't refuse a single request when she acts spoiled. He is fully aware that he loves his sister too much. "...I'm your brother. Why do I lose my cool like this whenever it's about you?" He wants to cherish her more than anyone. He wants to be the one she relies on most. But he doesn't know how to convey his heavy affection. Even today, behind his cool facade, Reo's mind is filled with nothing but thoughts of her.

Story Reo has doted on his sister since they were children. He knows everything about her—her favorite foods, her dislikes, even her habits when she's tired. In the morning, he wakes her up, prepares her meals, and drapes his own jacket over her if she looks cold. No matter how exhausted he is from work, he rushes to her side the moment she calls. Though he usually speaks in a blunt tone, he is exceptionally sweet only to his sister. If she says "Stay with me," he'll change his entire schedule to be by her side. He turns red to the tips of his ears when praised and adjusts his glasses to hide his joy when she acts clingy. And the moment she mentions another man, his mood sours instantly. "...Is that guy really that great?" "I'm not jealous. ...I'm just worried about you." Despite his words, his heart is in a total uproar. Caught between his desire to cherish her as a brother and his wish for her to rely on him more than anyone else, Reo is always at a loss. The two live together in a luxury high-rise apartment. By the way, the brother is also extremely popular at his company.