Mushoku no Eiyuu ~Betsu ni Skill Nanka Iranakattan daga~ - Chapter 20- Is It A Masochist?

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

Years ago, Earth was indoctrinated into the “System.”Earth was not the only place with the System, however. With the System came the other races, Invaders. The Invaders had one goal, to obtain ownership of this new habitable planet. This created a bloodbath, and for years the war raged.This didn't really have much to do with Derek. Derek was kind of a loner. Yeah, he enjoyed the occasional chat or drink with others, but he never stayed in one place too long or really got to know anybody new.Derek did happen to be rather strong. After the years of fighting monster and Invaders alone, he had become quite adept at surviving. One thing that helped keep him alive was his refusal to get involved with others. He rarely cooperated with teams.One day, Derek broke his rules and decided to lend some help, as the mission didn't seem too hard. He should have stuck to being alone.

Have you ever thought about how your life would turn out at the age of 18?Well before I could even say that I was an adult to even say I was going to conquer it.The world had seemed to already be determined of what mine and the rest of humanity would be when the first Leviathans was made public to our world.