God and Devil World - Chapter 666: The Allied Forces Appear!

A man reincarnates in the body of a boy who suffered a tragedy, only to realize that he is in the world of My Hero Academia. What's even stranger is that his quirk seems to have the abilities of Nen and Haki.

Jun Xie was the number one assassin in modern earth. His skills and knowledge in the field of assassination were unparalleled, his accomplishments unprecedented, his reputation terrified the entire underworld. However, during a mission to retrieve a mystical treasure, a mishap occurred…

He is now Jun Moxie, a sixteen year old super level debauchee, sole heir to the declining Jun family. A family of valiant heroes, left with an old grandpa, a crippled uncle and a debauchee as the sole heir! Accepting the world’s criticism and cold stares with a smile, his new journey begins! His life will be carved by his own will! Rise to the top! Evil Monarch Jun Xie!

“This cup I toast to those I’ve killed in my past life. Forgive me, for there is no chance for you to have revenge. Gulp!

This cup I toast to those whose life I will take in my new life. Forgive me, for you are fated to die by my hands. Cheers!”

- Description from novelupdates

Teela married King Heavenly because she loved him, but life in the Heavenly household was anything but euphoric. Lettie, her hard-as-nails mother-in-law, treats her like an unpaid servant. The family treats her like an outsider. King treats her like a shadow, transparent and forgettable.When Lettie presses Teela to prove her value to the family or get out, Teela has a decision to make. But she’s not leaving without a fight.King Heavenly rules Heavenly Industries with an iron fist, but he leaves his home life to his mother to manage, and that includes the management of his boring little wife. Teela has never complained. She’s never done anything interesting, for that matter. She’s just one more responsibility in a long line of responsibilities that King shoulders on a daily basis, and that is exactly how he treats her — as a responsibility that he’s delegated to his mother.Suddenly Teela steps out of the shadows and into a fight with him and his whole family, and King is baffled by the ruthless actions of his now daring wife. He’d always heard that vengeance is a dish best served cold, but Teela is coming in hot!