Crossovers That Should Not Be 18: You'll have SO MANY CROSSOVERS! 400 CROSSOVERS!

[Labster]

And no godless man shall sit in the Seastone Chair!

If the Seastone Chair is an accessory for game console, then this is already a Haiyore! Nyaruko-san crossover.
And while I'm on the topic...

Atlach-Nacha resembles a huge spider with an almost-human face. It dwells in a huge cavern deep beneath Mount Voormithadreth, a mountain in the now vanished kingdom of Hyperborea in the Arctic. There it spins a gigantic web, bridging a massive chasm between the Dreamlands and the waking world. Some believe that when the web is complete, the end of the world
will come, because it will create a permanent junction with the
Dreamlands allowing monsters to move freely into the waking world.

So if I'm reading this right, Mount Voormithadreth is at the D Point, and Atlach-Nacha completed enough of her web to allow Metalia to cross over from the Dreamlands?
-- ∇×V