I am a Gao Fushuai Villain - Chapter 596:

Li Pu, who has the blood of a summoned beast, originally just wanted to lie down honestly, but found that his talent as a summoner seemed a bit unusual…

- Description from novelbuddy

Transmigrating to the disciples of the Demon Sect, and relying on the skill modifier to become a giant of the Demon Dao.

[Detected the technique “Blood Nerve”, relying on devouring blood to practice]

[Side effects: easily affected by the spirit contained in the blood, becoming bloodthirsty, bloodthirsty, mad, and even brain dead]

[Please wait a moment, the system is being modified…]

[Ding! The modification is complete, and the side effects are cancelled]

- Description from novelbuddy

Wen Qinxi an IT guy at a prestigious gaming company lives a repetitive life, working on an innovative gaming system that is said to change the world. During a routine diagnostic check, he discovers a major flaw that could be detrimental but under pressure from the guys upstairs, the research and development hand over the revolutionary project despite Wen Qinxi citing flaws in the design. The CEO unaware of such a flaw enters the game as a test run before launching the product instigating a chain of events no one expected. manager: Wen Qinxii you have to go save CEO. You are our last hope Wen Qinxi: F*ck! l want a pay raise after this. Thus began the journey of saving the overbearing CEO

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.