Koyama, as named by Kozuki Oden and his retainers, is a white boar and the child of the Mountain God that lived in the forests of Wano Country as late as thirty years ago. In what became known as the Mountain God Incident, it was kidnapped from its parent and later stolen by Kin'emon.
Koyama is a young boar with white fur. When it first appeared, Koyama was a small piglet with round eyes and two short tusks.
Eleven years later, Koyama is shown to have grown larger than an average human.
After it was captured, Koyama was anxious and called to its parent for help. The Mountain God came to its piglet's aid, attacking and eating humans to do so.
At first, Koyama is treated relatively poorly by Kozuki Oden and Kin'emon. Despite this, Koyama and its parent eventually befriend Oden and his retainers and are given names by them, even helping Oden with his procession.
Abilities and Powers
Forty-one years ago, Koyama was kidnapped by a trio of men. The men planned to take it to the Flower Capital to claim a bounty of one platinum coin which was set on white boar piglets by the yakuza boss Kurokoma a year prior. On their way to the Flower Capital, the men stopped at a teahouse and showed off Koyama to a waitress named Tsuru. This conversation was overheard by a thug named Kin'emon who ambushed the men after they left the teahouse and stole the piglet from them. After arriving in the Flower Capital, Kin'emon came across a boy named Denjiro and showed Koyama to him. Denjiro warned Kin'emon about the parent of the piglet, known as the Mountain God, which is said to ruthlessly pursue its child if it is kidnapped. Just then, the two heard sounds of destruction caused by the Mountain God, and were approached by Kozuki Oden, who demanded that they give Koyama to him.
Koyama then began calling for its parent, prompting Kin'emon to tell it to be quiet. Oden insisted on taking the piglet, but Kin'emon protested as he still wanted to claim its bounty. One of Koyama's original kidnappers then found the group and warned Kin'emon that the piglet's parent ate his friends and Tsuru, which angered Kin'emon, causing him to drop Koyama and run off to fight the Mountain God. After Kin'emon was defeated, Oden held the piglet up in the air to attract the Mountain God's attention and used the opportunity to slice it in half, defeating it.
At some point after the Mountain God Incident, Koyama and its parent befriended Oden and his retainers and were given names by them. Thirty years ago, eleven years after the Mountain God Incident, Oden and his retainers went to the Flower Capital to hold a procession. A palanquin was strapped to Koyama's back and it carried Oden through the capital. Koyama's status and that of its parent are currently unknown.
- Koyama means "hill" or "small mountain" in Japanese. Koyama was given this name due to its small size in comparison to its parent, which was named Yama (山 Yama?), meaning "mountain".
- One Piece Manga and Anime — Vol. 95 Chapter 963 (p. 11-13) and Episode 962, An older Koyama is seen and its given name is stated.
- One Piece Manga and Anime — Vol. 95 Chapter 960 (p. 4, 6, 10, 16-17) and Episode 960, Kin'emon captures Koyama.
- One Piece Manga and Anime — Vol. 95 Chapter 961 (p. 2-15) and Episode 961, The Mountain God Incident takes place.