A nickname for a "villain" in the manga/anime Bleach, Ulquiorra Schiffer. It's a way of calling Ulquiorra cute and needy, like certain animes depict ukes. It is rarely used as an insult, and tends to be used by fangirls.
On a Bleach fanforum:
girl49370: I drew a picture of Ukelala in a bunny outfit!
girl2: Awww! So cute!