Kaisar is sentient.
According to Gou Inoue Kaisar is a sentient zombie because he was created by a bite instead of magic. It’s been said it might get an explanation in a follow-up OVA. There’s a problem though: It doesn’t apply to Genesis where all of Rita’s zombies are mindless drones regardless of how they’ve been created. And yes she did it by biting several times (eps 4 & 7 off the top of my head). Thus VS continues its glorious tradition of complete disregard of the previously established lore for fanservice.
But here’s a thought, why don’t we take this a step further and save Amira from Bahamut then? If there are no boundaries in rewriting the canon so why not just do that?