4.3 MSQ Ending:
It's clear that Zenos probably did a body swap with an Ascian, as his soul is now in the Katana-wielding Soldier, evident by how he was able to unleash a burst of aether from swinging his blade, and his banter about continuing the hunt from the one who defeated him. I imagine the Ascian infiltrated the Empire a while ago and made a pact with Zenos that should he be defeated, they will resurrect his body and swap bodies with him to further their goals. Only Ascians deal with summoning, so it's very clear that an Ascian is possessing Zenos' body, like how Lahabrea did with Thancred. What's more is that Zenos is always simple-minded and has a 1-track mind, whereas the "Zenos" we see in Asahi's flashback is a soft-spoken, well-spoken, and cunning man, as opposed to Zenos' gregarious style of speaking.