Subaru, a transfer student, comes to the school to take piano lessons from the genius pianist, Soushi. However, his true identity is that of a hitman targeting Soushi's father, Hiroshi. Staying at "Hotel in Humans," Subaru, along with Ikuro and Sara, prepares to assassinate Hiroshi. As the day of the assassination approaches, Subaru becomes increasingly engrossed in playing piano duets with Soushi. The piano, which was initially just a tool to get closer to his target, Hiroshi, unconsciously transforms into something irreplaceable to Subaru with each duet he plays with Soushi.
