Once Ace understood that the corpse vessel hadn't vanished because it wasn't part of the mirror persona, because it was never supposed to, and the scripture did exactly what it was designed to do: steal the soul and reproduce it faithfully.
His eyes darkened with understanding as he thought, '…I neglected the fundamentals!'
Now Ace was an Undead Soul, for a brief moment, frustration flickered through him as his plans had derailed. His timing had been tight. Any delay here was dangerous.
But the frustration didn't last because another realization followed immediately after he thought about the five corpse vessels he had just stored away, and a sharp glint passed through his soul-light eyes as if realizing something extremely important.
'…If I'm an Undead Soul now…' He thought as excitement was creeping into his otherwise calm reasoning, '…then all I need is a body. Should I try to use Corpse Possession?'
