It's an idle RNG(random chance) minigame. Watch the characters fight! Wins are shared across all players.
Hover here for more info.
Click and drag to move the camera around! All characters have the same chances of winning. It's all random. Character Lv = shared number of wins of that character.
Chrome preferred. Try clearing your cache if the player is not loading.
Also check out the RPG Battle YCH 1 & 2!