Usotsuki Method

Rikka has never been able to forget about her ex-boyfriend, Kazuto, from middle school. Even though they go to the same high school, Kazuto won't even look at her, let alone talk to her. Meanwhile, Kazuto has lost his memory from his second year of middle school onward...!? A heart-warming love story filled with the feeling of youth!

(Source: Shogakukan, translated)