One Piece: Here Comes A Jin!

[Marines + Medium-Slow Burn + Hand-to-Hand Combat + Great Swordsman + Split Personality + God-Slaying in the Late Game + Momonosuke Must Die]

A teacher who was angered to death by his students in class transmigrates to the world of One Piece and becomes the young Gin.

Can killing villains make you stronger? Then if I eat a Shichibukai today and a Four Emperors member tomorrow, does that mean I'll have to eat the Pirate King the day after?

Oh, I nearly forgot. There's also the Celestial Dragons...

Tesoro: "I'll pave the stairs to godhood with gold for you!"

Bullet: "Aside from Roger, you're the second man whose strength has made me submit."

Golden Lion: "Damn it, is there really a man in the East Blue even crazier than Roger?"

Dragon: "Mentor Gin, the Revolutionary Army will follow in your footsteps for the sake of our shared ideals!"

Five Elders: "Damn it, Sengoku, what are you Marines doing? The Marines are supposed to serve the Celestial Dragons and the World Government!"

Sengoku: "Show some respect, you little punk. We Marines serve under the King of the World, Gin!"

Only when the man riding a wind dragon lorded over the skies above Mary Geoise did everyone realize his true ambition!