Warp is evil when he wears the headpiece, which slots in to where his memories are supposed to be, and is only referred to as Warp when he was evil, e.g. from Neiro or from the baby-like person (who's name evades me right now) in episode 5; when he is not wearing it, he is referred to as Kaiba and he was together with Neiro without it.
Kaiba and Popo duel with Popo shooting him in the body, and resulting in him falling from his palace. Neiro (as we see in her memories) falls down to save him with a baloon attached. As it's an electrical cloud, he loses his memories (see episode 1--the balloon people), but Neiro does not as she as a green barrier around her head. (Which the ostrich in episode 1 also had.)
Something happens to Neiro when they hit the ground and is taken in by Popo. The Memory Merchant may or may not have copied her memories before Popo paints over them. If so, it could be in Hyo-Hyo but it's rather holey-- e.g. Hyo-Hyo is more than capable of writing down who she is or what not.