Kappas

Kappas are a mythical species that appear in The Menagerie trilogy.

Description
Kappas are an aquatic mythical species that are known to be mischevious. They only speak in Japanese, so only those knowing the language, such as Kieko, can understand them.

The Menagerie
Blue owns a pet kappa, who he keeps in his room. When Logan first stayed overnight at the Wyoming Menagerie, Blue showed him the kappa. Blue noted that the kappa spoke only in Japanese and that Keiko sometimes talked to it. Blue also recommended that if the kappa ever challenged Logan to an arm-wrestling competition, he should just say no.