Komasaburo (Japanese: コマさぶろう Komasaburou) is a character who debuted in Yo-kai Watch the Movie: Lord Enma and the Five Tales, Nyan! in Episode 3.
Komasaburo is a small infant with pink cheeks, some brown hair (in close resemblance to that of Nate's), has some baby fat and has a tiny nose as well as a large mouth. Like most babies, he wears a diaper.
Komasaburo first appeared in the second movie, as Koma Mom tells Komasan and Komajiro that they have a new baby brother to the family. Koma Mom also told the Koma brothers "He doesn't drink much milk, and his mood's been awfully foul, zura...", in which Komajiro has to pinpoint that the baby is a human.
As Komajiro asked where did Komasaburo came from, Koma Mom answered his question with "It was a gift from the gods, zura!", which made Komasan realize the real mother of Komasaburo must've been worried sick about him. When Koma Mom turns around, she notices the baby is missing, and Komasan, Komajiro, and Koma Mom eventually found Komasaburo in the ceiling board. Realizing Komasaburo could get hurt, Komasan gets up there to get the baby safely down, but Komasaburo falls from a wooden plank (which Komasan "dragged" to prevent him from falling).
Koma Mom saves the baby by having him land on her squishy body, but however, the fall on her caused Komasaburo to fly up higher. After Komasaburo eventually landed on a long plank, Komasan noticed him while saying "MONGE~!! Wait for me, zura!!" and tried to help Komasaburo get down, but is encountered by a giant Dromp (unknowningly summoned by Lord Enma) which first sucked up the baby and started to destroy the tower they're in. Komasan and Komajiro shockingly at first have no idea how to save Komasaburo, but Koma Mom eventually gave a solution to the Koma brothers by saying they have to pull the baby out.
Komasan was right when he noticed a shining object on top of the Yo-kai, and goes to get it, but falls off and is saved by Koma Mom, who boost him up higher to the top of the Dromp's head. He eventually found the object and pulled it out, turning back into Komasaburo, and also causing Dromp returning back to normal without any memories of the event.
In the ending, Komasaburo was reunited with his parents after Koma Mom returns him to them.
"Komasaburo" combines Koma and Saburo meaning "third son".