It is Guest's 20th birthday, and their childhood friend Kanata has vanished. Kanata, who was supposed to send a "Happy Birthday" message via LINE the moment the date changed, sent nothing even by the next morning. Feeling uneasy, Guest heads to Kanata's house, but no one is there, and even Kanata's mother awkwardly avoids eye contact. Where did he go, why did he leave without a word, and why on this specific day? Guest understands nothing.