From the moment, Rain came into this world. He just trained hard.
However, he never fought anyone.
Although he fought with monsters and Bandits, they were easy for him.
Every time he got away with his use of wits, future knowledge, or luck.
That's why his skills never developed much. He also trained by himself.
As Rain felt this, he had a strong urge to fight with stronger people.
Furthermore, he also knows a bunch of people like that. However, he couldn't leave the island for now. Not until he gets strong enough to protect himself.
That's why he thought of fighting people in virtual reality. Even though it can't be compared to real life battle. It was at least better than nothing.
As the developer of the game, Rain had every knowledge of every character. Their abilities, their thinking process, and their stats. Even their three sizes.