Rebirth of the Ultimate Master (2021)

Blurb:
What happens when a former martial emperor gets reborn into a complete loser’s body? Scott Dillon, a legendary martial artist who was ranked third-strongest in the continent, finds himself in this predicament when he wakes up in the body of 15-year-old Kerwin Walton. Kerwin was once a failure who had yet to open a single chakra portal in his body, but now he’s morphed into a genius martial artist overnight and becomes the talk (and target) of the town. Armed with the expertise of his former life, Kerwin is on a mission to complete the ultimate incantation that killed him in the first place – all while wiping the floor with his former bullies at school. Will Kerwin be able to exceed the accomplishments of his previous life? One thing’s for certain: no one will ever call Kerwin a loser again!

Source: www.anisearch.com/manga/84790