Oyamatsumi is the god described in Japanese mythology. Another name is Watashi no Okami or Sakatoke no Kami. There are not many descriptions about Oyamatsumi himself, but the god called the son of Oyamatsumi sometimes appears in the myth.
Descriptions in Japanese mythology
In Kamiumi (giving birth to gods), Oyamatsumi was born between Izanagi and Izanami. Later, he and Kayano-hime, the god of the field, bore eight gods forming four pairs as follows.
Amenosazuchi no Kami, Kuninosazuchi no Kami
Amenosagiri no Kami, Kuninosagiri no Kami
Amenokurado no Kami, Kuninokurado no Kami
Otomadoiko no Kami, Otomadoime no Kami
Masakayamatsumi no Kami
Odoyamatsumi no Kami
Okuyamatsumi no Kami
Kurayamatsumi no Kami
Shigiyamatsumi no Kami
Hayamatsumi no Kami
Harayamatsumi no Kami
Toyamatsumi no Kami
In the fighting with Yamata no Orochi, Ashinazuchi and Tenazuchi, whose daughter Kushinada-hime later became the wife of Susanoo, said that they were children of Oyamatsumi. Then, Susanoo and Kamuohoichi-hime, who was a daughter of Ohoyamatsumi, had sons, Otoshi no Kami and Ukanomitama, as described in Susanoo's genealogical table. On the other hand, Yashimajinumi, who was a son of Susanoo and Kushinada-hime, married Konohanachiru-hime and Fuhanomojikunusunu was born. Okuninushi is the descendant of Fuhanomojikunusunu.
After tensonkorin (the descent to earth of the grandson of the sun goddess), Ninigi met the daughter of Oyamatsumi, Konohana no sakuya-bime, and then Oyamatsumi gave Konohana no sakuya-bime and her older sister Iwanaga-hime to Ninigi. However, Ninigi sent back Iwanaga-hime only because she was ugly, and Oyamatsumi got angry at that, saying "I sent Iwanaga-hime wishing the eternity of Tenson (the grandson of the sun goddess) like an unchangeable "iwa" (rock). But he sent her back, so the life of Tenson will be short."
In the names of gods, 'tsu' means 'no' (of) and 'mi' means god, so 'Oyamatsumi' means 'the god of oyama (big mountain).'
In another name Watashi no Okami, 'wata' is an archaic word meaning sea, and this name represents the god of the sea. Therefore, he is the god of both the mountain and the sea as represented by his names. Additionally, it is described that Oyamatsumi was pleased when Konohana no sakuya-bime bore Hohodemi, and he made amenotamu-zake for offering to the gods, and this also made him Sakatoke no Kami, the god of sake. Further, he is believed to be gunshin or bushin (the god of war).
Oyama Afuri-jinja Shrine (Isehara City, Kanagawa Prefecture), Umenomiya-taisha Shrine (Ukyo Word, Kyoto City), and all Mishima-jinja Shrines and Ozumi-jinja Shrines (大祇神社) throughout Japan are dedicated to Oyamatsumi. The head shrines of Mishima-jinja Shrines and Ozumi-jinja Shrines (大祇神社) for all parts of Japan are Oyamazumi-jinja Shrine (Omishima-cho, Imabari City, Ehime Prefecture) and Mishima-jinja Shrine (Mishima City, Shizuoka Prefecture), respectively.