Kimi wa Houkago Insomnia centers on Ganta Nakami, a high school student whose nights are ruled by insomnia and whose days are often shadowed by exhaustion and irritability. At school, he is always looking for a quiet corner where he can catch a brief nap, while the people around him only see his sharp temper and withdrawn attitude. Across the halls of the same school, Isaki Magari seems almost his opposite: bright, sociable, and easy to approach, yet she is hiding her own sleep disorder from everyone else.
Their paths cross in the abandoned observatory once used by the school’s astronomy club, a forgotten room that becomes a secret refuge for both of them. When Ganta discovers Isaki sleeping there, the two recognize in each other the same frustration, loneliness, and fatigue that come with being unable to rest. As they begin to share the observatory, their unlikely friendship grows into something gentler and more meaningful, giving them a place to talk honestly, recover their energy, and face the everyday pressures of school life together.