In the MCU/Marvel with the Omnitrix/Ultimatrix - Chapter 38: New Aliens, New Fun

One day, I woke up only find out that I’d become a Demon Lord, an individual responsible for protecting a dungeon. The world I’d been spirited away to was one filled with violence. Gigantic monsters wandered through it and competed with each other each and every day for the right to survive. I had no choice but to strengthen my dungeon’s defenses in hopes of living another day—or at least that was what I’d thought. For some odd reason, I instead ended up spending my days in relaxation and bliss.

“No way, Salino, you said that this little guy who killed 300 million pirates in one blow, who is only eight years old this year, is your biological brother?!”

Sengoku Marshal’s office, Akainu, Aokiji, Garp, Sengoku, Crane, all looked confused. “It’s really him!”

Huang Yuan was also shocked and confused, his younger brother was obviously only eight years old, how could he be so fierce? ! At this time, summer is here. Sengoku invited him to join the navy.

“Joining the navy is no problem, I want to be an admiral!”

Red Dog frowned: “General? Just you?” Xia Tian made a decisive move, and sent Red Dog flying with one punch, shocking the audience!

“Yes, it’s just me.”

- Description from novelbuddy

Some people begin their lives with the odds in their favor but end up failing miserably.

Lin Jingzhe, having suffered many losses and setbacks, returned to his eighteen-year-old self just before failing his college entrance exam.

Business opportunities were everywhere in the early 1990s when the Chinese economy started taking off.

Now, this golden age would be his.

- Description from Novelupdates

After struggling in the apocalypse for ten years, Yao Ran died and returned to the three months before everything began. She returns with hatred and thirsts for revenge, intent on making those who owe her pay with their lives.With her grandfather's inheritance, Yao Ran sold everything and frantically hoarded weapons, medicine, food, and supplies. She sharpened her sword, stockpiled up supplies, settled scores with scoundrels and villains, and repaid them with both enmity and kindness.When disaster strikes, she begins her revenge, facing a dangerous world, and is determined to outlast her previous life.