Transmigration: Into the Life of Severus Snape - Chapter 61 - 58: A Seal of Power

When a fantasy kingdom needs heroes, they skip the high schoolers and summon hardened Delta Force operators.Lieutenant Cole Mercer and his team are no strangers to sacrifice. After all, what are four men compared to millions of lives saved from a nuclear disaster? But as they make their last stand against insurgents, they’re unexpectedly pulled into another world—one on the brink of a demonic incursion.Thrust into Tenria's realm of magic and steam engines, Cole discovers a power beyond anything he'd imagined: magic—a way to finally win without sacrifice, a power fantasy made real by ancient mana and perfected by modern science.But his new world might not be so different from the old one, and the stakes remain the same: there are people who depend on him more than ever; people he might not be able to save. Cole and his team are but men, facing unimaginable odds. Even so, they may yet prove history's truth: that, at their core, the greatest heroes are always just human.

A broken man who ended his own life finds himself reincarnated into the game he used to play. However, instead of becoming the protagonist or a powerful antagonist, fate places him in the role of a minor villain—a mere stepping stone for the protagonist in the game's first arc.

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.

The story is about a a hitman, Who dies because of his own recklessness and transmigrates into a game he used to play after his retirement as a hitman.I'm not gonna spoil any further, but i might answer few of your questions.Is MC overpowered?Nope, he'll become strong over time and all battle he'll fight will be because of his effort and techniques.Is there magic and adventure?Yes! It have both magic like normal isekai with adventure and fighting with monsters and many other things. There are other important things like “Essence Stone” But let's talk about it in the chapters.There will be harem?Not really, He will be in contact with many beautiful female and males but one waifu but i haven't decided yet.All i can say is, give it a try, I'll try my best to make it worth your time.