i dont know for sure but im pretty sure its connected to the reason why he's in the game to begin with even tho he's an actual human. At the beginning of the story when he's playing the game he comes across this super powerful boss and it kinda breaks the fourth wall by looking at him through his phone and then he got yanked into the game.... from what i can remeber so i just assumed that whatever that superboss thing is, is whats causing the difficulties to change. Maybe its trying to kill him maybe its trying to see if he's a good candidate for an overarching plotline ╮(￣▽￣)╭
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OH! Honestly I forgot that dude even existed, makes sense
Spoilers!
This is from what I know in the next floor challenges
It is similar to his bifrost swords ability = the interference power or idk what its name (where it can be used to manipulate some points in the floor)
Wherein, the boss in the 80th floor was able to used interference power and they choose to rebel from the goddess and fight to gain their freedom back by killing the heroes.
Very suspicious that every boss level that Han is apart of turns into Nightmare difficulty. Is it just him, is he simply unlucky, or is it because he keeps taking on the side missions? Guess we'll have to wait for the next few chapters to see if anything swanky happens