Reincarnated As Poseidon - Chapter 39: Long time Ago (poseidons past)

Before going to college, an ordinary high school student went to celebrate and got drunk. When he woke up, he found himself in a completely different world. There was a big sect, the approaching sect entrance examination, a slum where his body’s previous owner lived, and a shared memory about a missing young girl.

When he got tangled in a fight with a few punks in this different world, he fell off a cliff and miraculously found himself still alive, with two more voices ringing inside his head. They were Sword Master and Saber Master. In the company of them, he continued to find out more about this whole new world. He took the sect entrance examination, entered the sect, met a strange man in black, and even participated in a major competition of the sect to have a chance to win over his peers!
In this whole new world, he was born again and got to explore the fantastic martial world!

- Description from Novelupdates

“There are no heroes. In life, the monsters win.”

...

In 2106, [Mayhem Online], a fully immersive VRMMO game, was released. Soon, it dominated the world's economy when people could exchange the in-game currency with real-life currency and vice versa.

In the year 2107, Flynn Grey, a 22-year-old college dropout with an ambiguous history, joined in the fray of billions of people that had already started playing [Mayhem]. Hoping to uncover the game's secret and earn a fortune, he spent months on adventures without fruitful results.

For better or worse, Shura, Flynn's in-game character, ends up in a great Wyvern's den, acquiring a hidden class and a monstrous race. Join him as he defeats his past and paves his way into becoming a true legend in both worlds.

Lucas is a homeless teenager who had everything taken away from him— his family, his home, his childhood. Even worse, he was born without any abilities in a world where humans with superpowers dominate.

All of that would change when a new dungeon appears before Lucas.

Thinking that it was a sign the gods have given him— that he should just give up and end himself, Lucas enters this dungeon without hesitation while expecting death.

However, inside the dungeon was not the end like Lucas had expected.

Instead, it was the beginning of his life of carnage.

Wielding the power of a «Hero», Lucas begins his journey of vengeance on the world that stole everything from him.

Are you humiliated by being attacked?

Are you sorrowful to be a stepping stone?

As a cannon fodder hanging in two episodes, are you unwilling?

Don’t worry, I am here!

As the only system supplier of All Heavens and Myriad Realms System Shop, I can make a variety of portable systems for you, and let you reach the peak of your life!

Boy, it’s time to raise your eyebrows!

Boy, it’s time to counter-attack!

- Description from Novelupdates