Seems like they're preparing a new part of Time Temple.

So we're just gonna ignore the fact that the video clearly takes place in the Temple of Time?

Being shown right after you create the character doesn't necessarily indicate a chain of events.
They shoved a TV commercial into their game.

Temple of Time is pretty much floating right on top of Leafre, where they end up...

Demon Slayer does attack the Black Mage too. Right before he's knocked out and sealed in an energy draining machine in Leben.