Isawa Kuzushi

Isawa Kuzushi was a shugenja of the Phoenix Clan of the 10th century who named Kuzushi no Oni.

Banished
Kuzushi was a powerful shugenja who was banished from the Isawa upon accusation of dealing with Oni and other foul creatures.

Summoning an Oni
Angry with her former kin he sought revenge summoning an Oni. In a hidden manor house named Mori Kuroi, deep within the Isawa Woodlands, he performed the ritual while a Solar Eclipse was happening. In return for his name the Oni taught him powerful maho.

Shiba incident
Kuzushi moved to Shiba lands, and with time he gained his trust. He was selected to preside over the wedding of Shiba Tsatsuro and his betrothed, Asako Reiha. Kuzushi felt a passion for Reiha and tricked Tsatsuro, convincing him that his bride to be was unfaithful. Reiha committed seppuku after the groom made his claim in public. Later Reiha's oldest brother discovered the role played by Kuzushi, and the shugenja was banished from the Shiba lands.

Remorse and Death
Kuzushi realized his association with th Oni was destroying his life, so he tried to send the demon back to Jigoku. Instead, in his pride and naivete, he set the Oni free, being killed by the creature.

Black Forest
The oni free went on rampage until the Phoenix finally managed to banish it. The lodge where it was first summoned, became blackened as the monster was dragged back into the Shadowlands, and the place was known as Mori Kuroi, the 'Black Forest'.