Moto Cheat ☆ Makeppanashi

Washinami Ui harbors a secret: he remembers his previous life as an invincible knight. Now, he’s just a small, thin high school boy dealing with a stalker. On his first day at his new school, he unexpectedly reunites with Leonhardt, his rival from that past life, and vows to keep a low profile. But out of nowhere, Leonhardt kisses him! With no recollection of their former lives, Leonhardt has transformed into a flamboyant and flirtatious guy named Shishiou Leon, the exact type of person Ui detests!

(Source: Taiyohtosho Company, translated)

Note: Chapter count includes an extra.