That is some next level dirtiness.
Hmmm, i am really curious where in the timeline this story pass, we know Kohaku is one of the four devil kings (was that the name?), and they sure can live a lot so it isnt exactly impossible that this is the past but at the same time all this surreal sword stuff was never mentioned in the first series even during Asudora past arc.
I can picture two possible explanations: this is the future or this is another continent. The "another continent" theory in reality could support this story being in the past.