Naruto: Starting with Infinite Chakra - Chapter 20: Lightning Flame Blade and Lightning Chakra Transformation

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

Somebody once told a joke.A man ran in place all his life. He worked a job he didn't love for people he couldn't stand. But at the end of the day, the number in his bank account went up.That man got a second chance at life. He woke up in another world, full of adventures and romances and monsters and gods. And floating above his head he saw the number “1”. So what did he say?“Gosh I better make the number go up.”Not today. Not for this old soul. Reborn as a beast of battle meant to live a short life and die screaming, Garek refuses. He puts the madness of skills and levels behind him and sets out to found a little farmstead. He grows crops. Maybe someday he'll get a pig, and have bacon.It's a shame the world won't let him be. It's a shame that the warmongers and level-grinders hate nothing more than a soul at peace.He put down his sword for a plowshare, but when trouble comes calling, he'll pick it up again.

In the year 54 of the Konoha Calendar, two super geniuses appeared in the Konoha. One is named Uchiha Itachi, and the other is named Akihara Kagura. One is a tool of the village, willing to sacrifice everything for Konoha, except for his brother Uchiha Sasuke; the other claims to be a tool of the village, also willing to sacrifice everything for Konoha, including Uchiha Itachi's brother, Uchiha Sasuke.

Born of a great family, world shaking genius.