Legendary
Traditional Yokai

Koga Saburo

Koga Saburo

Also Known As
Koga Saburo
Category
Half-Human / Half-Yokai
Personality
A brave and relentless seeker. Even when cast into the abyss by the jealousy of his own blood, he continues to forge ahead through the underworld, and even after transforming into a serpent, he never loses his resolve to return to Suwa.
Origin
Koka District, Omi Province (around present-day Koka City, Shiga Prefecture) / Mount Tateshina (present-day Nagano Prefecture) / Suwa Taisha
NaganoShiga
  • Mount Tateshina─ 諏訪縁起で甲賀三郎が妻を追って入る穴の舞台となる信濃の山
  • Koka District─ 甲賀三郎の名が示す近江国甲賀郡。物語上の出自を示す
  • Ōmi Province─ 主人公甲賀三郎諏方の本貫である近江国甲賀の上位地名
  • Suwa Taisha(諏訪市中洲)─ 蛇身化した甲賀三郎が諏訪明神へ結びつけられる信仰圏
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Basic Description

Koga Saburo is the protagonist of a medieval Japanese legend found in the "Origins of Suwa" chapter of the Shintosho, recounting an epic subterranean journey and his transformation into a serpent. Described as the third son of a powerful family in the Koka District of Omi Province, he enters a deep cave in Mount Tateshina in Shinano Province while searching for his missing wife, Princess Kasuga, only to be trapped underground due to his older brother's jealousy. After a long and arduous wandering through the subterranean otherworld, he finally returns to the surface, but his body has transformed into that of a giant serpent or dragon, ultimately linking him to the worship of the Suwa Upper Shrine's deity[1]. Rather than conflating him with Takeminakata-no-Kami from the Kojiki, Koga Saburo is best understood as the product of an alternate medieval Suwa origin myth—an archetypal story of "a warrior who attains godhood by passing through the form of a serpent"[2].

Folklore & Legends

The core of the Koga Saburo legend features elements of a hero's descent into the underworld, fraternal jealousy, the search for a lost wife, transformation into a serpent, and his ultimate deification as the Suwa Myojin. In her study of the source material for the story "Gyofukuki", Kyoko Aoki treats Koga Saburo as a "Koga Saburo turned Dragon" legend linked to giant serpents, Suwa, and the *Tale of the Koga Saburo Cave*[3]. Additionally, Yuko Tagaya categorizes the Koga Saburo legend under the AT301 tale type of the international folktale classification system, focusing on the structural elements of the subterranean realm, the otherworld, adversaries, and the hero's return for comparative research[4]. In the Edo period, the story was adapted into a *joruri* puppet play known as the *Tale of the Koga Saburo Cave*, expanding its influence beyond Suwa mythology into the realms of Koka, Iga, and traditional performing arts[5].

Related Yokai

Yokai deeply tied to this one in legend.

Detailed Analysis

The fascination of the Koga Saburo legend lies not merely in its heroic epic, but in how it explains the origins of Suwa Myojin as "the return of a mortal who fell underground." Unlike Takeminakata-no-Kami from the Kojiki, who retreats to Suwa as the defeated figure in the myth of the transfer of the land, Koga Saburo travels from Omi to Shinano, falls into the underworld through a cave on Mount Tateshina, and returns as a serpent. The deity of Suwa does not simply descend from the heavens, nor does it merely arrive from central mythology; it manifests by passing through mountain caves, subterranean kingdoms, and the body of a snake. This narrative beautifully weaves together the elements of Suwa worship—water, mountains, dragons, serpents, hunting, and the syncretism of Shinto and Buddhism—into a single tale. This is precisely why it is meaningful to establish Koga Saburo as a distinct figure alongside the official enshrined deity Takeminakata.

Character Profile

This section is our own creative profile for storytelling. It is not historical fact or scholarship.

Personality
A brave and relentless seeker. Even when cast into the abyss by the jealousy of his own blood, he continues to forge ahead through the underworld, and even after transforming into a serpent, he never loses his resolve to return to Suwa.
Compatibility
He resonates strongly with Takeminakata-no-Kami, Suwa Taisha, Mount Tateshina, the Mishaguji deities, Moriya-no-Kami, dragon and serpent gods, and tales of subterranean otherworlds.
Abilities
The endurance to traverse the subterranean otherworld on footTransformation into the form of a giant serpent or dragonUnification with the deity Suwa MyojinConnecting the husband-and-wife myths of the Upper and Lower Shrines
Weaknesses
As he belongs to a medieval origin myth distinct from the Kojiki's Takeminakata-no-Kami, oversimplifying them as the exact same deity can lead to misunderstandings.
Habitat
Koka District in Omi Province, the caves of Mount Tateshina, Suwa Taisha's Upper and Lower Shrines, and the areas surrounding Lake Suwa.

For more detailed information and diagnosis results about Koga Saburo, the Serpent Deity of the Underworld, please click here.

Sources & References

5
  1. 神道集 — 安居院作、貴志正造訳（平凡社・東洋文庫94, 1967）　[中世説話集]中世神道説話集。甲賀三郎が地底を巡り蛇身となって諏訪明神へ結びつく「諏訪縁起の事」の基本文献。
  2. 諏訪信仰の中世:神話・伝承・歴史 — 福田晃、徳田和夫、二本松康宏編（三弥井書店, 2015）　[研究書]諏訪信仰の中世的展開を扱う論集。『神道集』内の諏訪、諏訪縁起の変容、中世神話としての諏訪明神像を確認する。
  3. 『魚服記』の素材--『甲賀三郎』をめぐって — 青木京子（佛教大学大学院紀要29, 2001）　[研究論文]大蛇、諏訪、『甲賀三郎窟物語』、龍になった甲賀三郎伝説を論じる研究論文。甲賀三郎の蛇体化・龍蛇性を確認する。
  4. 『熊のジョン』を媒介とした『ベーオウルフ』と話型AT301『甲賀三郎伝説』との関連について — 多ヶ谷有子（関東学院大学文学部紀要126, 2012）　[研究論文]甲賀三郎伝説をAT301型の成熟した形として比較説話研究の中で論じる論文。地底異郷譚としての構造確認に用いる。
  5. 甲賀三郎窟物語 — 竹田出雲、文耕堂（山本九右衛門ほか, 1735）　[近世浄瑠璃]享保20年初演の浄瑠璃作品。中世諏訪縁起の甲賀三郎伝説が近世芸能へ展開した例として用いる。

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