The "singularity of the sea" that Seahamut created based off of albacore. Her unique nature caused other fish to avoid her, leaving her all alone in the ocean until she met her brother, Tunaro. Her beloved brother gave her the name "Neruko" because of an idiom about sleep and growth in some language. She used to stay in Tunaro's mouth because she feared the outside world, but now does so merely because of her affection for him. She measures her growth daily by comparing her size against Tunaro's teeth.
