
Quick answer — Kyouko Chikiri voices Kappa in Natsume's Book of Friends Season 1, Stua in Ultramarine Magmell.
Kyouko Chikiri voices Kappa (Natsume's Book of Friends Season 1), Stua (Ultramarine Magmell).
Kappa is voiced in Japanese by Kyouko Chikiri.