MTL - The Fallen Merman - ~ Once Upon a Spellcaster: The Golden Apple

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.

Kaiden Tian’s aspirations of basketball stardom take a heartbreaking turn when a car accident not only claims his mother’s life but also robs him of his ability to walk. Undiscouraged, he settles for a role as the waterboy of a top high school basketball team, determined to stay close to the game he loves. However, he meets an untimely death and finds himself inhabiting the body of Kai Guo, a notorious troublemaker blessed with an ideal physical form. [Welcome to the Rise to Legend System!] With this second chance at life, Kaiden sees an opportunity to rewrite his destiny and fulfill the dreams that were once shattered.

The ill-fated high school student Liu Yuan obtained the inheritance of the top civilization in the universe and changed his own destiny. He also used many powerful technologies in the inheritance to lead the Chinese nation to rise in the universe.

- Description from novelbuddy

The royal bastard of House Vasquer, Argrave, changed after his stay studying magic at the Tower of the Gray Owl.

The sickly man's awkward posture and cruel behavior have been replaced with a neat dignity and acerbic wit.

Though once listless, he now strives towards his goals with a life-or-death tenacity.

Most come away thinking he seems to know too many details about too much. Few can claim to know his motives or his goals.

Yet behind that confident appearance, the primary contributor for an open-world RPG's wiki battles existential dread and things far beyond his ken as he struggles to adapt to a grim, gothic fantasy world mirroring his favorite game.

The prospect of fighting against a world-ending calamity loses all of its appeal when it transitions from entertainment to reality.

Argrave is spurred towards unwanted heroism to preserve his life as he struggles desperately to keep this sinking ship afloat.