And imagine home he want to go back is actually same world he saved but way in the future
And then the 100 worlds he was visiting was actually the same world, just different eras and/or maybe parallel versions of it.
Then by, saving those worlds he is preventing a more devastating world ending catastrophe in his far far future.
Then, knowing this, his far far future sends him to that white space to create the paradox(?) / eternal cycle to save the world.
HAHAHA, sorry. It's kinda fun to pull theories out of my ass sometimes.
It should be fine as long as I only do it w/fiction :)))
"Use external mana to power up your magic"
She used probably almost all of the demonic realm mana so I guess that place is almost bare in mana now.
And they were trying to use the same technique to place teleportation magic devices in many places.
I think they will make their world magic-less in just a few years.