Manga/Manhwa in Which The MC is Secretly Overpowered (OP).

1. Mercenary Enrollment.

At the age of eight, Ijin Yu lost his parents in a plane crash and became stranded in a foreign land, forced to become a child mercenary in order to stay alive. He returns home ten years later to be reunited with his family in Korea, where food and shelter are plenty and everything seems peaceful. But Ijin will soon learn that life as a teenager is a whole other feat of survival. With only one year of high school left, Ijin must master new tactics to maneuver his way around the schoolhouse battleground. Can he survive a year of high school? Or rather, will the school be able to survive him?

An overpowered and skilled Veteran mercenary kid has to act as a normal high school boy. What more do you need?.

2. Memorize.

Korea's first ever webnovel of the 'another world' genre, Memorize. The legend has returned in webtoon form!] Hall Plain, a different world from Earth. After being discharged from military service, Kim Su Hyun is suddenly abducted to the world of Hall Plain. After many twists and turns, he manages to reach the peak of the Hall Plain. However, all the anguish he had experienced during his 10 years in the Hall Plain left him in despair. To change his bitter past, Kim Su Hyun decides to use the Zero Code's power to turn back time 10 years. "It is absurd to use an object with such incredible power to simply turn back time. I will ask for the final time. Player Kim Su Hyun, do you truly wish to repeat those ten years of torment?" Seraph looked at me like she was pleading. I couldn't help but laugh for no particular reason. For no particular reason indeed.

An overpowered Veteran player who has ended the real life game went back to time and acts as a first time player.

3. The Max Level Hero Has Returned!

Struck by an enemy’s arrow, the powerless Prince Davey O’Rowane falls into a coma. His soul travels to a place where the greatest of the great gather—the honorable Hall of Heroes. There a thousand years pass as Davey undergoes excruciating training under their watchful eyes to become a hero too strong for his own good. Now back to his timeline and his kingdom, he’s wide awake and the enemies hiding in the king’s court better be prepared. The prince they had dismissed is now their biggest threat!

Prince while being in coma, he became the strongest and when woke up he acts as a weak prince. An overpowered prince acting weak.

4. My Dad Is Too Strong.

A scatterbrained, talentless civil servant returned as the heavenly Demon. He now wished to live the rest of his life peacefully, as his days in the Murim world were full of conflict and bloodshed. However... "Please be my father until I graduate." He suddenly gained a daughter out of nowhere.

The strongest warrior is reincarnated back to his original body and acts like a normal civil servant. An overpowered civil servant dad.

5. Volcanic Age.

Joo Seo-Cheon, a man who survives the age of war through sheer luck, becomes Hwasan faction's elder only to live a life full of regrets and doubts. He then lies on his death bed waiting for the inevitable when he is returned to the past…

MC went back to time and now he knows everything but he is hiding from everyone this fact. An overpowered martial arts master.

6. Spy X Family.

Master spy Twilight is the best at what he does when it comes to going undercover on dangerous missions in the name of a better world. But when he receives the ultimate impossible assignment—get married and have a kid—he may finally be in over his head! Not one to depend on others, Twilight has his work cut out for him procuring both a wife and a child for his mission to infiltrate an elite private school. What he doesn’t know is that the wife he’s chosen is an assassin and the child he’s adopted is a telepath!

This is a very special family but they are trying to act as a normal family. An overpowered spy family.

7. Trash Of The Count’S Family.

When I opened my eyes, I was inside a novel. [The Birth of a Hero]. [The Birth of a Hero] was a novel focused on the adventures of the main character, Choi Han, a high school boy who was transported to a different dimension from Earth, along with the birth of the numerous heroes of the continent. I became a part of that novel as the tr*sh of the Count’s family, the family that oversaw the territory where the first village that Choi Han visits is located. The problem is that Choi Han becomes twisted after that village, and everyone in it, are destroyed by assassins. The bigger problem is the fact that this s*upid tr*sh who I’ve become doesn’t know about what happened in the village and messes with Choi Han, only to get beaten to a pulp. “…This is going to be a problem.” I feel like something serious has happened to me. But it was worth trying to make this my new life.

MC isekaied to a story which has read, he knows the future but he hides from everyone this fact. An overpowered main character who knows the future.

8. The Live.

Half a year ago, Yun-jae Kim lost his wife and daughter in a car accident, and lives in despair day after day. One evening, his diary completely erases itself, leaving behind an ominous message: "you can see them again". 'The 'Holy Grail' is given to those who overcome the 'game' of 'The World of the Backside', and it is said that if you use it, you can reunite with your lost family ... In the cruel world where only the strongest survives, Yun-jae becomes the only one who knows the future. Will he be able to fulfill his wishes?

MC is reading about the future so he knows everything but he hides from everyone this fact. Another overpowered main character who knows the future.

9. Hero? I Quit A Long Time Ago.

Zero was mankind’s first real superhero. Under his watch, countless other superheros appeared and followed in his footsteps. However, after 5 years of war, Zero disappeared without a trace.

The strongest hero got bored and now acts as a normal citizen. An overpowered Hero.

10. Gosu.

A young man set forth to avenge his master, a once powerful martial artist who was betrayed by his own men and barely escaped with his life. Armed with his master's supreme martial art techniques, he is ready to bring terror and wreak havoc among the murim. But before he even got started, he learns that the ones who had betrayed his master are already dead... Erm, so what happens now?

He was trained to become the strongest and now acts as a normal citizen. An overpowered martial artist now a common citizen.