Masamune-kun's Revenge

Masamune-kun's Revenge is a manga series that received an anime adaptation which aired in 2017.

The story follows Masamune Makabe, a handsome and fit high school student who was a chubby boy when he was younger. Eight years ago he had a close relationship with a beautiful wealthy girl named Aki Adagaki, until one day she cruelly rejected him and gave him the nickname "Pig's Foot". Seeking revenge, Masamune changed his name and lost weight, and now he has returned to make Aki fall in love with him so that he can reject her as harshly as she did back then, helped by the fact that she doesn't recognize him when they reunite.

OP
Masamune takes his shirt off at the beach.

Episode 1
Masamune has just finished his workout.

Episode 3
Masamune works out.