Imouto ni Kiite Minai to

A high school student named Daichi Fukumori fabricated a story about having a younger sister to bond with a girl he liked. After deciding to confess the truth, a girl unexpectedly shows up and addresses him as her older brother. To his shock, this sister is real, and the situation quickly becomes more complicated than he anticipated. Daichi realizes he needs to speak with his sister before things escalate further.