From A Stronghold NPC To The Final BOSS - Chapter 1009 - : What’s wrong?

Shangjing Hospital’s intern, Xiao Yifei, stumbled upon some scandalous behavior from the chief doctor and subsequently faced the hostility of the chief, making his work life extremely difficult. Little did he know that shortly after, Xiao Yifei would inherit the legacy of the Jade Dragon Eye. X-ray vision, control, all within my sight. Lolis, beautiful women, all within my embrace. From then on, Xiao Yifei embarked on a life that was nothing short of spectacular!

In the world of One Punch Man, the seventh S-class hero of the Hero Association, the King Engine King has obtained the super god skill system.

As long as you have reputation, you can extract the skills of the heavens and the world!

DNF’s extreme swordsmanship, the flames of fire in the god of death, the Tensei and Samsara in Hokage, the top three-color domineering in Pirates, the dragon slaying magic in Fairy Tail… Look at the system panel. For the 100 million prestige balance, KING took a discount and chose Stud. “Ding!”

- Description from novelbuddy

This novel is also known as Only I Level Up

10 years ago, after “the Gate” that connected the real world with the monster world opened, some of the ordinary, everyday people received the power to hunt monsters within the Gate. They are known as “Hunters”.

However, not all Hunters are powerful. My name is Sung Jin-Woo, an E-rank Hunter. I’m someone who has to risk his life in the lowliest of catacombs, the “World’s Weakest”.

Having no skills whatsoever to display, I barely earned the required money by fighting in low-leveled catacombs… at least until I found a hidden catacomb with the hardest difficulty within the D-rank catacombs!

In the end, as I was accepting death, I suddenly received a strange power, a quest log that only I could see, a secret to leveling up that only I know about! If I trained in accordance with my quests and hunted monsters, my level would rise.

Changing from the weakest Hunter to the strongest S-rank Hunter!

- Description from Novelupdates

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.