[ZeroToMaru]

This have a theory that Vice is not ikki's True demon
His demon is probably is deep in his body
It might probably part of Giffus body
So Vice probably like just a normal demon
It will probably control Ikki
Something like Evolto with Sento in Build
Joining or taking over Ikki's Body in the end Vice and Ikki will
Unite and that will be the
Super form or Being controlled by "True Inner Demon" the Berserk form like
The hazard form or and
Be the super form after regaining Ikki's mind
So that is just my theory