The "he" the Mirror Person referred to was the Sauron Family's ancestor, one of the spirits left after the three-in-one Red Angel evil spirit had split apart following the battle at George III's mausoleum, when the Betrayal charm struck it while it was connected to all the mausoleums.
When the loosely assembled evil spirit broke apart, one of its components escaped with the explosion, while another entered the depths of the mausoleum and vanished. Only Sauron's evil spirit had accidentally crashed into the Mirror World. Angel's Mirror Person had taken him into the City of Calamity, and he had been unable to leave if he wanted to survive.
But why had he been able to leave the City of Calamity and the Mirror World on his own this time and return to the Physical World? According to the Mirror Person, without any Beyonder characteristics inside him, wasn't his Spirit Body liable to dissipate at any moment, erasing him from existence?
Looking at the smiling Mirror Person, Angel suddenly thought of a possibility:
"You bestowed some Hunter powers on him as a boon?"
The Mirror Person nodded slightly.
"That's right. After advancing to Catastrophe, our control over the Sefirah's power strengthened further, allowing us to bestow Hunter or Demoness powers up to Sequence 3. What I gave him was the power of a War Bishop.
"Of course, under normal circumstances, bestowing a boon burdens the bestower. Even true gods rarely use this method, preferring to gradually cultivate ordinary Beyonders through the potion system instead... As for the recipients, the imprint contained within the boon to prevent its power from gradually dissipating also affects their minds and bodies. It amounts to a controllable, retrievable form of corruption.
"Do you remember that Navy Admiral's mistress on Oravi Island? Her ordinary human body directly