The design of Fafnir's Tail is inspired by a dragon in Norse mythology who was transformed from a dwarf. Fafnir is the eldest son of the king of the dwarf world, and since birth, he has had countless wealth. But his desire for wealth is inexhaustible. After being lured by wealth, he killed his father and turned into a dragon to monopolize the treasure. His heart also has magical powers, if you can eat his heart you can get immense wisdom, can understand all the things in the world. If soaked in Fafner's blood, you can make the body become invulnerable to swords and spears. If you can get Fafnir's body, you will get infinite power.
In the nautical world of SWISOK, Fafnir is cursed with sexuality for monopolizing treasure. When the curse came, his tail would swell with an insane lust for sex, and Fafnir slapped and rubbed his tail against the cliff but couldn't quench his thirst. Fafnir's pain ceased only when he heard the groans of travelers and those who wanted to steal the treasure.