Lancer-class Servant seen in Fate/Grand Order during the Lostbelt arc. Caenis is a woman who was raped by Poseidon. Afterwards, Poseidon granted her a wish; Caenis wished to become an invulnerable warrior. Poseidon granted her wish, turning Caenis into Caeneus. Along with her physical body, her name changed into Caeneus to differentiate between the two.
