Mako Maruyama (丸山真虎 Maruyama Mako) is the assistant of the Witch on top of Horned-Owl Mountain. He either fights or gives a riddle to anyone trying to enter the Witch's house
Prior to the events to the series Maruyama was a famous Sumo wrestler named "The Volcano", he was considered the greatest wrestler in the ring until killing an opponent during a match. After killing his opponent he was disqualified and left unemployed. He spent the remainder of his years fishing near the Redfox Coast.
During the events of Cowa! he encounters Paifu and Josei who attempt to find scares near his raft. During his encounter with the two In spite of becoming acquainted, Maruyama teases Paifu and picks up two sticks producing a cross gesture to scare him off believing he, like some vampires in stories, fear a cross. On the contrary, this action forces Paifu to transform into a rampaging were-koala. Though before he is mauled Maruyama is spared from Paifu's rampage as Josei reveals that Paifu turns back to normal after being exposed to a round object. As they get acquainted Maruyama revealed to the two monsters about his past and confirms that he did murder his opponent which cost him his title. Later on in the story when Paifu's village has come down with an epidemic called "Monster Flu" Maruyama is recruited by Paifu to help get the medicine they need from Horned-Owl Mountain. Maruyama agrees to help only if he is paid 1,000,000 yen for his troubles so that he can purchase a large boat. However he is deceived by Paifu as he tells him the villagers will pay him. During their journey they begin to bound with Maruyama revealing his first name and earning the nickname Mako-leen. While stopping for supplies Maruyama later encounters a group of thugs who start a fight with his monster friends and ends up overpowering them. Eventually Mako and the monsters eventually reach Horned-Owl Mountain. While in the forest Apron comes down sick with "Monster Flu". They leave him with a family that live in the woods and learn from them about Baibou a monster that guards the woods from trespassers and is weak against whistling.