Action

Free to read on Webtoon titled "Teenage Mercenary"
A plane crash left him as the only survivor and Ijin works as a mercenary in a foreign country to survive. After an encounter with the Korean military he is able to return home. All Ijin wants to do is be a high school student and live peacefully with his family but there are many factors preventing him from doing so

One day "Gates" began to open around the world connecting the real world to a monster one. On this day people all around the world were given powers to fight the monsters and became "Hunters". Sung-Jin Woo, an E-Rank Hunter (the lowest rank), during one of his missions his life changes forever
The art and plot of this story is really well done. The MC starts off super weak and slowly becomes over powered. This is definitely a must read action manwha

This is free on webtoon called Viral Hit
From the same author as Lookism
A bullied kid finds old Newtube videos teaching people fighting techniques. He decides to start his own channel, making great content and learning how to fight.
The author's art is stunning. They also do a great job of fleshing out the side characters. I enjoy the added backstories because they provide more depth to the story.

A mercenary is killed by his own men on a mission. He wakes up three years later in the body of a high school student in Korea. Now he wants to find out the truth and get revenge
This is good except the author does add unnecessary "love interests" as in he isn't interested in them but they are in him

The MC has this super strong ability but he relies on it too much and his life goes downhill once it disappears. After having a dream of the future he decides to take a deal and go to another world called the Lost Paradise.
The MC is strong, smart, and stays true to his values.
This could possibly be a harem in the future because it's a harem novel (from what I've heard). BUT so far the comic has removed most of those scenes

He finds out his brother was killed after being betrayed by his friends in the Obelisk, the Tower of the Sun God, a world where several universes and dimensions intersect.
A revenge story, where the MC goes to kill everyone who hurt his brother. He's pretty OP and gains a lot of powerful allies.

The MC receives a S-Rank skill that allows him to randomly choose one skill from his opponent. But he can only choose a skill after he is killed.
I read part of the novel for this as well and I feel so bad for the MC because this guy dies so many times just to get things right. If I were in his shoes I would've gone crazy so props to him for being so strong willed