Rōen

is a legendary monster resembling a cross between a tiger and a wolf.

Background
In the past, Rōen frequently attacked the Howling Wolf Village, killing its villagers by absorbing their chakra. The Kodon clan was able to defeat Rōen by sealing it into their clan's shrine. Time passed and Rōen became a myth.

Decades later, when the Howling Wolf Village began contemplating declaring neutrality, Tenma Kodon released Rōen from the shrine. Using saigenzai to control it, Tenma had Rōen attack the village in order to sway the villagers against neutrality. During the village's defense, however, Tenma lost control of Rōen because of the Kumanoi clan's blue fire powder. He and his wife tried to seal it back into the shrine, but his wife was killed and he could not perform the seal by himself. After failing to to seal Rōen into his oldest son, Reishi Kodon, Tenma sealed it into his youngest son, Kina Kodon. Tenma dies in the effort, leaving only Reishi to know that Kina contains the monster.

Abilities
Though similar in size and power to a tailed beast, Rōen is merely an animal, driven by instinct instead of intellect. It can live forever so long as it absorbs chakra from others, which its does with the many tentacles that sprout from its back.

Part II
For ten years, Rōen lies dormant within Kina's body. As Kina is increasingly picked on by the villagers of the Howling Wolf Village, however, Rōen takes advantage of Kina's growing anger to take control of his body and absorb the chakra of those who pick on him. Reishi is each time able to subdue Rōen before it can kill anyone else or completely consume Kina, and for a while the villagers remain unaware of Kina's involvement. When Kina transforms in front of a mob, however, Rōen is able to launch an assault against the village. It nearly succeeds in at least taking full control of Kina, but Reishi, with help from Sasuke Uchiha, is finally able to seal it back into the Kodon clan's shrine.

Though the village is saved, Reishi's seal will only last for seven years, at which time Rōen will return. Kina intends to be there when it does so that he can do all that he's able to stop it.