Not sure actually. It should function the same as any other enemy and be dependent on having enough MP to cast the spell. Maybe there's something in that pre-battle, the unknowns are, well, unknown. I don't even know if they were in Karifean's script or if it's something I added later for whatever reason.
Death handling is an animation of sorts, and I don't think characters have it. You could try copy-pasting Dyne's Death Counter AI in, and then trying to find Red XIII's death idle animation index (replacing the one Dyne uses in this AI). Not tried that myself, but could do the trick.
The other guys are:
RTDA: Cloud
RUDA: Tifa
RVDA: Aeris
RWDA: Red XIII
RXDA: Yuffie
RYDA: Cait Sith
RZDA: Cid
SADA: Sephiroth
SBDA: Barret (Melee)
SCDA: Barret (Shoot)
SDDA: Barret (Cannon)
SEDA: Barret (Alt Shoot - Microlaser)
SFDA: Vincent (Handgun)
SGDA: Vincent (Shotgun)
SHDA: Vincent (Rifle)
SIDA: Cloud (Hi-res)
SJDA: Galian Beast (buggy, doesn't work the same way as characters)
SKDA: Death Gigas (ditto)
SLDA: Hellmasker (ditto)
SMDA: Chaos (ditto)
Two things; the weapon won't appear with the character, or else it'll appear in some odd place (Red XIII doesn't have a weapon so it's not noticeable), and the transformations like Galian, etc. can be used (I saw a vid using Chaos as a base) but I don't have notes on it.