Seventeen-year-old Yuichi Ezaki is spending his days in a hospital in Ise, Mie Prefecture, recovering from hepatitis A. Frustrated with his confinement, he frequently tries to escape, only to be caught and disciplined by the nurse Akiko Tanizaki. During one of his excursions around the facility, Yuichi notices a beautiful girl his age in the east wing and learns from Akiko that her name is Rika Akiba. The nurse strikes a deal with him, agreeing to overlook his attempts to sneak out if he agrees to befriend Rika, who has spent most of her life hospitalized due to a weak heart valve.

As Yuichi gets to know Rika, he finds her to be selfish and demanding, but he soon understands that her difficult personality masks the fear and loneliness of her condition. Their fragile relationship begins to blossom despite significant obstacles. Dr. Goro Natsume, Rika’s physician who harbors his own complicated feelings for her, tries to keep the two apart, motivated by his painful past of losing his wife to a similar illness. Adding to the drama is the elderly patient Yoshizo Tada, a perverted old man who acts as an unlikely mentor to Yuichi, encouraging him to pursue love without regret. When Tada suddenly dies, his final will leaves his enormous pornographic collection to the young man, creating further comedic complications with Rika.

Realizing the seriousness of Rika’s condition, Yuichi decides to help her experience the world outside the hospital walls. With the help of his loyal friend Tsukasa Sekoguchi, who dons a zebra mask for secret missions, Yuichi orchestrates an escape to take Rika to Mount Houdai for a breathtaking view of the night sky, where they share their first kiss. In another notable arc, Yuichi arranges for Rika to borrow a school uniform and visit a real classroom, granting her the simple dream of experiencing a normal student life. Through these adventures and the meddling of the hospital staff, the two teenagers learn to confront their feelings and the uncertain future together.