Summoner: Monster Girl Harem! - Chapter 179 4: True Colours.

A bitter old man gets tossed into the world of Tamriel, as a descendant of a religious madman no less, watch as he delves into the secrets of magic and explores the wonders of this danger-filled world, and with luck and a lot of magic juice possibly even beyond.This is my first attempt at writing a fanfic (or anything for that matter). English is not my native language but I think there shouldn't be too many mistakes. The story will focus on magic and exploration with most likely a bit of romance later on.

There is no master god, no system, no exchange, and some are just source codes that are fused in the mind to open up the world, not to be forced or suppressed, but to constantly go through in order to become powerful Look at my infinitely powerful source code …

- Description from uukanshu

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.

This story is about a god level player, Li Cangyu, who returns to the game Miracle after being away for several years. The story explores him playing the game and setting up a team in an attempt to finally win a trophy in the Miracle Professional League.
E-sport God Series 1 “The Strongest God”
E-sport God Series 2 “God Level Summoner”
E-sport God Series 3 “The King’s Return”