HxH: God of Choice System - Chapter 351: Ninjutsu Collision

A supreme expert in the Immortal World had died, and a strand of his soul returned to its original body on Earth. Tang Xiu discovered with amazement that ten thousand years passed in the Immortal World, yet only a single year passed on Earth.

Ruthlessly betrayed by his lover and trusted friends, Tang Xiu found that his soul went back to his previous body on Earth, and, despite he spent 10,000 years in the Immortal World, just a year has passed on Earth and many things have changed. Having an unsurpassed knowledge, Tang Xiu will protect his loved ones and go back to the Immortal World to take his revenge.

- Description from Novelupdates

"When will people understand.... I'm only half insane?"

In regards to the MMORPG Cross Reverie, Sakamoto Takuma boasted an overwhelming strength that was enough for him to be called the Demon King by the other players. One day, he gets summoned to another world with his appearance in the game. There, there are two people that insist “I am the real summon master.” Takuma gets slave-turning magic used for summoned beasts cast on him by the girls –

The end of the world is full of crises, but Su Chen says not to worry because he has the Red Alert System. That’s how confident he is. You say you have a lot of weapons? Sorry, I have more weapons than I can use here. Let me introduce you to the weather control device. You say the mutant beasts are very powerful? No problem, I have a way to deal with them…