Sera and her brother Sam live alone in a rented apartment in Tokyo. Sera is in love with her brother's best friend Nathan. She takes some advice from her friend and finally decided to confess her love to Nathan ,at the exact moment Sam , Nathan and his class mates who are senior had a industrial visit for a week in Okinawa island .While saying farewell to her brother Sam while the bus was moving, she sees Nathan in the window seat and loudly confesses her love to Nathan, Sera did not hear what Nathan responds was as the bus was too fast. Sera waited for a week for Nathan and her brother to come back from the tour but they never came it seems that the bus had gone missing. After a month Nathan was found in the forest of the island and was brought back. Sera who heard this went to the hospital to meet him but turn out Nathan had lost all his memory no one's know what happened to the people in the bus? Sera daily before leaving to college meets Nathan n leave him a lunch box and while going home takes the lunch box home Nathan doesn't even talk to her or sees her face it's been a week since she been doing that and today strangely Nathan has not eaten anything from her lunch box she open the lunch box and finds a letter and a drug hidden in it. The letter says dont trust anyone ,Sera is confused and puzzled at the very moment some one rings the door bell .Is the letter a clue to find her brother?Will she be able to find the missing bus?Did Nathan actually lose his memory and who's at the door ?Many mystery remains unsolved