One Piece: From the Rocks Era to King of the World - Chapter 362 - : Death of Saint Maz, one of the Five Elders

In a mass ambush at the Battle of the Gods, the four major guilds with all their armies surrounded one man alone: McRae, known by all players as the God of War.

But even the God of War could not survive alone against hundreds of attackers.

Yet, when McRae opened his eyes again, he’d returned to the first-day launch of the game, [Divine Domain]- and he still had his full-level character, with all classes available to him to switch freely between at any time.

With all his previous memories, McRae knew that their entire world would soon merge with the game world, where death would become permanent… And so he turned on Divine Domain once more– this time fully aware of every detail about the players, the treasures, and the game itself.

Before the four guilds were even formed, McRae would have a guild and an army of his own.

Gods and demons fought, the worlds collapsed, only eternal immortal realm, lasting in the world.

After eternity, a god of war named Zhao Yun condensed the heavens and the earth, recast the cosmos, from the blue to the earth, marked the eternal immortal realm, in the name of the god, the king is over the world.

Since then, what he said is a myth.

- Description from MTL

Genius, antisocial, solitary, intractable , maniacal.

At the turn of every era, it is he who raises the flag of the rebel cross.

Winners take it all, losers take the fall.

He who brings order to a chaotic world, assembles talents and masterminds.

He who hides among the crowd, yet stands on the top of the world.

— The one and only, him.

- Description from Novelupdates

Another entry in what you can call the Proto Harem Series: the books written before the Harem Series that take place in the same world.

It’s about a swordswoman whose student is captured, so she goes to rescue her.