User blog comment:NightmareLorelei/Do anyone suspect a Water/Sea Dragon Slayer?/@comment-7405046-20151111132029

I think Hiro will keep the number of Dragon Slayers (aside from Acnologia) at 7, due to symbolism. Also, a Water Dragon Slayer (Wendy) was considered and discarded already, so that specific element will be even harder to see, I guess, except for maybe an easter egg-like reference.