Chaldea sends in Ollerus instead of Ritsuka to try and resolve each of the Singularity, Pseudo-Singularity & Lostbelts. If Ollerus somehow fails to resolve a Lostbelt or Singularity, ROB teleports him to the next one and his journey begins again. Can Ollerus resolve all the Singularities...
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Funnily enough, assuming Goetia doesn't just retgone him at the start due to sensing how powerful he is, I could actually seem him doing decently well. Though Zeus, Cernunnos, and Oberon should be major road blocks for him to deal with.
What is essentially Presence Concealment that even let him sneak up on Othinus (for what its worth), and the God-Killing Stake/Turn Into a Fairy spell (which also worked on Othinus), he shouldn't do too bad.
He's not making it all the way even with moderate wank though.