Aside from the two newly acquired skills, it seems that when the three masks came together and Hannya first ascended to Arajin, she comprehended a unique skill that was subsequently completed—
[Ghost Mask·Three-faced Void: Three faces as one, universal laws in void. Hannya summons a void embodiment and merges one of the abilities held by the three masks to alter the void's form. The effect of the void's abilities is many times stronger than Hannya herself.]
It was certainly good news that the unique skill got completed, but Kamiyagawa went over the description provided by *Strange Tales* twice and still felt puzzled.
"Summoning a void embodiment?"
Void embodiment, in principle, is a term from the Buddhist sect.
Its meaning pertains to "illusion, emptiness."
Summoning a void embodiment likely means conjuring a sort of illusion.
As for why the youkai Hannya could have ties to Buddhism, Kamiyagawa had some clues.
