Kei Kusanagi isn't your typical 15-year-old high school student. He's actually an 18-year-old with a rare disorder that puts him into what he calls, a "standstill". When he was younger, this disorder left him in a deep coma which stunted his growth for three years. Mizuho Kazami isn't your typical teacher, either. She's actually an alien sent by the Galaxy Federation to observe the Earth! As the sole human being with knowledge of Ms. Kazumi's secret, Kei must... marry her?!