Yapool comes out of Ultraman Ace (1972 - 1973) Aparently they are a race/species of monsters. So I'm guessing that if it's convenient for the plot, we might get more.

(Randomly, I'm assuming that Mirai's comment that he and his brothers defeated Yapool was a reference to the movie? Though I didn't think that Yapool was in the movie...? *is somewhat puzzled*)

Going back to being productive in real life, rather than in research.