Jun Jiuling - Chapter 27: The Reason for Doing This

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.

When an S-class elite assassin-raised captain of a special ops suicide squad comes home from a high-stakes Africa mission, he finds himself offered something that could potentially set him up for life- a curious assignment that he could use to finally exit his days of war and slaughter.

Then placed into a high-school setting, Lin Yi is tasked by the chairman of a top-tier multi-billion company with bodyguard duty for non-other than his own daughter, a certain little Miss of said high-school.

His enemies, once ranging from drug lords, mafia bosses, political figures, and national leaders, are soon replaced with spoiled kids who happen to have rich papas and mamas, and Lin Yi finds his intense expertise and high-threat skillset misused, and very underwhelmed…

But he does get a harem cast as diverse as his old enemies, so Lin Yi decides that, for the sake of messing around with girls as an invincible entity in a down-leveled environment, leaving his bloody and death-filled war days behind is something he’d definitely want to strive for.

- Description from Novelupdates

What is a genius? Capable of comprehending any battle skill regardless of the skill itself and sweeping away the bottlenecks while cultivating a new technique; this is a true genius! He Yiming was originally an ordinary youngster in the He family’s estate with not too extraordinary aptitude in learning martial arts.

After mistakenly pointing all the attribute points to the treasure drop rate, Xiao Shi found that every time he kills, he will drop an item.

A mosquito was slapped to death, and a pill fell out.

After killing an evil spirit, a cheat book fell out.

Hacking a martial artist to death will drop out the opponent’s cultivation experience.

…

- Description from novelbuddy