Natsumi Tachibana lost her 19-year-old younger sister Haru to an illness. Haru had a fiancé called Tougo. Despite it being an arranged marriage by the parents, Natsumi knew that Haru genuinely liked Tougo when she was alive. However, after Haru's passing, Natsumi agreed to date with Tougo, with the condition that Tougo brings her to all the places he went with Haru. Despite this, Natsumi feels guilty about dating Tougo. Is Tougo a curse left to her by Haru?
