En Oyashiro

is a shinobi and arms dealer from the Chinoike clan. He would occasionally attend the Coliseum as a patron in order to collect kekkei genkai.

Background
As a member of the Chinoike clan, Oyashiro lived in the Valley of Hell with his wife and daughter, Chino. Although their clan had been able to live in the valley peacefully for many years, being constantly in such close proximity to each other eventually caused disagreements between clansmen to erupt into violence; only Oyashiro and Chino survived. Oyashiro regretted his role in the deaths of his clan, especially his wife's, and wished for Chino to grow up to be better than he was. To that end, he took advantage of Chino's young age by concealing his relationship to her, instead telling her that he had her entire family killed so that she would become the last possessor of the Ketsuryūgan, and thus a valuable commodity.

Oyashiro took Chino from the Valley of Hell and started making a career for himself as an arms dealer. He trained Chino to be a combination of bodyguard and means to resolving "business disputes". He also began collecting young children with kekkei genkai such as Fūshin, adding them to his bodyguard retinue and providing them the care they needed. After a few years in Oyashiro's service, Fūshin fled with Chino and the other children in his collection; although Oyashiro claimed to feel betrayed, he was glad that they were forging out on their own.

Fūshin went on to form the Lightning Group, which targeted Oyashiro a number of times and forced him to withdraw from public appearances, instead sticking to his various secret hideouts. He would still sometimes attend the Coliseum when he learned of a kekkei genkai user competing there, hoping to win them for himself.

Personality
Oyashiro is a greedy and eccentric individual who only cares about collecting kekkei genkai owners in exchange for money. Oyashiro found it to be easy to kidnap small children, to keep up his habits compared to kidnapping adults. He would raise these children into growing up as violent and merciless shinobi to increase the powers of their abilities, as well as make them more impressive to his potential clients. His cruel treatment towards his victims caused him to become a target of hatred from them and they envisioned getting revenge on him, but he finds these feelings unworthy. Oyashiro seems to care less about his status as a criminal and he retorts at Sasuke for once being one when the latter criticised him for exploiting people. Orochimaru comments that En is hopeless when it comes to Chino, his precious daughter, whom En would go at great lengths to protect. It is also commented by Orochimaru that, despite seeming to mistreat her, En is a doting parent to Chino.

Appearance
Oyashiro has beige hair, a moustache, a goatee, and violet eyes. His clothing consists of a baggy light brown tunic that is decorated with green and khaki stripes along each hem, underneath which he wears a teal shirt and pale green pants. He dons a red headband under his hair and large diamond-shaped sunglasses. Oyashiro also wears a pink bangle around his right wrist and a pair of plain flip flops on his feet.

Abilities
As a member of the Chinoike clan, Oyashiro possesses the Ketsuryūgan. He credits the fact that he has never starved to his medical ninjutsu, as it always places him in demand. In the anime, Oyashiro single-handedly killed his entire clan, implying great skill.

Sasuke Shinden: Book of Sunrise
Oyashiro learns that Sasuke Uchiha, the last possessor of the Sharingan, is going to compete in the Coliseum. Oyashiro decides to take part and enters Futsu in a fight against Sasuke. Futsu loses, which, per the rules of the Coliseum, means that Oyashiro must forfeit ownership of Futsu to Sasuke. Sasuke declines to take Futsu, instead asking Oyashiro what he knows about Fūshin. Oyashiro complies.

Despite Oyashiro's attempt to characterise himself as a compassionate caretaker of Fūshin, Sasuke criticises him as being an exploitative child slave owner. Oyashiro doesn't feel it's appropriate for Sasuke to be finding fault considering that he's made no attempts to help any of the slaves competing in the Coliseum. Sasuke concurs, so challenges Futsu to a rematch. Sasuke beats Futsu again, as well as all the other competitors who challenge him, thus winning their freedom. Oyashiro is amused by Sasuke and so tells him Fūshin's last known location in the Land of Water. In the anime, Oyashiro provides the information about Fūshin as thanks for Sasuke's help in stopping an attack by exploding humans.

The Coliseum is later raided by Chino (Sasuke in the anime) and its patrons are all arrested; Oyashiro is able to escape unnoticed. He meets up with Orochimaru afterwards, noting how proud he is with how Chino has turned out. Because his arms dealing business has been brought to an end by the raid, he muses about converting the Valley of Hell into a hotspring as his next enterprise.

Trivia

 * Oyashiro derives from the Japanese shrine Izumo Ōyashiro, which is known for matchmaking for business and personal success.

Эн Ояширо