Yamata no Orochi

Yamata no Orochi (ヤマタノオロチ) was a legendary snake god and the personification of the Hi'i River in Izumo.

About
The people of Izumo believed that the Hi'i River was a benevolent snake god for bringing the rains that watered their rice fields. When heavy rains would cause the river to flood, drowning residents and destroying their crops, the people began to see Yamata-no-Orochi as a violent deity. The ghosts of the victims continue to haunt the river.

According to legend, Yamata-no-Orochi, with a flood, consumed and killed Inada-Hime, the deity of the rice fields, so Susano'o descended to Mt. Senzu and slew Yamata-no-Orochi. From one of the snake's tails appeared the Ame-no-Murakumo-no-Tsurugi.

After undergoing grueling training in Izumo and reaching the peak of Mt. Sentsu, Ryu and Tokageroh use the legend of Yamata-no-Orochi as inspiration for further development of their Over Soul.

Trivia

 * It is a common misconception that the "Yamata no Orochi" is a second spirit that Ryu possesses.