—This is modern Japan, a normal world with cars and smartphones—

In this world, while Guest was walking down the stairs, they were pushed by "someone" with great force and fell. Due to that accident, Guest became paralyzed from the waist down, forced to live in a wheelchair and rely on others for daily care. One day, Guest's older brother, Shion, hears about the accident. Learning that Guest needs help with everything, the kind Shion decides to move in with Guest. He handles everything from housework to nursing care without a single complaint, but he is overprotective, enforces strict rules, and has one room that must never be entered.