The Extra is a Genius!? - Chapter 474: Silent Rings

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

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

Gu Ji, a cadet at the SWAT Academy, downloads a game called Crisis Management. After he clicks it, he has been thrown into the game's world. After he beats an instance, the same event would happen in the real world.“Your Choice：Stamina Boost (Small)】or【Combat Specialization (Small)】”

The MC transmigrates to the Narutoverse in the body of an orphan boy from the Senju clan, as a normal person from modern Earth he has little to no fighting experience, but luckily time is something he has a lot as Naruto is just 6 months old so, he can slowly build his strength to live a “Peace-full” life