RAIDS ONLINE: RAGNAROK BEAST - Chapter 27: Why Are You Here?

Read the first chapter. You will probably like it. ;)

Reborn into an ancient world of hardship, Chen Qing became a scholar who toiled through ten years of cold study, finally achieving fame on the golden list. Just when he thought he'd join the ranks of the literati, marry a beauty, and reach the pinnacle of life, he suddenly found himself entangled in a bizarre and fantastical incident.It was also at that time that he discovered this world was far from simple—there were man-eating demons, heart-bewitching devils, and even the legendary immortals who could live forever but were exceptionally strange!What he found even more inconceivable was... these deadly things seemed... to all have been designed by himself!!!

The end of the world is coming, the world has undergone great changes, and everything has changed. Plants, animals, and even insects, as long as there are living things, have mutated.
Become more powerful, and even evolved supernatural abilities, such as chickens and ducks that can fly to the sky, such as cats and dogs that can breathe fire.
But only humans, without any obvious changes, seem to have fallen from the top of the food chain to the bottom of the food chain overnight.
Any creature that can open its mouth to eat can treat humans as food.
But fortunately, this world has not completely killed humans. Gradually, humans discovered that they had the ability to cultivate compatibility with other creatures.
As long as it has a high degree of compatibility with some powerful mutant creatures, it can be used for its own use to achieve the purpose of protecting itself.
Fang He is a person who is very compatible with mutant animals, but it is also because of his ability that he has changed from the strongest to the stupidest.
Fang He, who was reborn, said, “Hmph, this time…”

- Description from novelbuddy

An ordinary (?) grandfather, Choi Chuntaek. In an effort to protect his granddaughter, he started the virtual reality game 'Arkstar.'

Then... he accidentally obtained a legendary class?