@AcKyuubi
For me it was the transition from page 22 to page 23
"He predicted this course of action and waited there"
"Shit, I lost the others"
Welp, boss battle ensues.
@HammerU89
It's not like he was practicing combat magic every day for thousands of years. He secluded himself only fanatically researching subjects he was personally interested in, which IIRC took a whole lot of time for each project.
@lovolo
AFAIR a whole bunch of people all over the planet were summoned into "the tower" with the only way to return to the normal world being to conquer all the tower's levels.
It appears as though beings from other worlds/realities have kinda the same thing going on and apparently one or...
Surprised the enemies weren't some giant rabbits/rabbit monsters/rabbit demihumans to reference the "Holy Hand Grenade of Antioch":
https://www.youtube.com/watch?v=ashgP4YMdJw
@Your_dad_is_disappointed
Remember when at the beginning of this manga he was stranded in the "underworld" for years constantly fighting and annihilating the "Majin"? That's his claim to fame over there as it were.