En Oyashiro

is a medical-nin and a kekkei genkai collector.

Background
The majority of Oyashiro's past is unknown. He became a medical-nin but he developed a keen interest in people who possessed a kekkei genkai. His obsession led him to kidnap several shinobi from various villages and hold them captive so that he could earn money from rich people who wanted to hire such shinobi for missions. He would also stage fights between different shinobi with his clients in attendance to determine which was the strongest in an arena called "Coliseum". This earned Oyashiro to be condemned as a international criminal and he went into hiding in various hideouts, similar to Orochimaru, who admires him and has met him at some unknown point in time.

In the anime, Oyashiro is a survivor of the Chinoike clan and he slaughtered the entire clan, sparing only Chino, who is his daughter. His reason for this act was to protect Chino from the clan's desire for revenge against the Uchiha clan, therefore to protect his daughter from the cycle of hatred and bloodshed if the Chinoike clan had acted out its vengeance. To further protect her, he successfully concealed their familial bond by leading her to believe he kidnapped her and his reason for making her enter into Coliseum competitions was to help her grow strong enough to defend herself.

Personality
Oyashiro is a greedy and eccentric individual who cares more about collecting kekkei genkai owners in exchange for money. Oyashiro found it to be easy to kidnap small children, such as Chino, 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. In the anime, 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 his seemingly unfair mistreatment, En is a doting parent to Chino.

Appearance
Oyashiro is a beige-haired, goatee'd man with 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
Most of Oyashiro's abilities are unknown. All that is known is that he is a strong medical ninja. In the anime, as a member of the Chinoike clan, Oyashiro possesses the Ketsuryūgan, which allows him to control the blood of his opponent upon direct skin/eye contact and excel in genjutsu. Even more, the fact that he slaughtered his entire clan single-handedly further implies great might on his part.

Plot Overview
Sasuke and Orochimaru arrive at the Coliseum to meet with Oyashiro, whom Orochimaru says likely has information on the Dark Thunder Group and the original Lightning Group. Oyashiro is hosting a tournament, and upon seeing Sasuke's Sharingan, he abruptly names Sasuke as a participate with the hope of obtaining it, much to the latter's dismay. He sends his best shinobi, Futsu, to fight Sasuke and Futsu is quickly defeated. Sasuke demands for the information he desires, and Oyashiro explains that Fūshin (the leader of the Lighting Group) became his protégé after losing a match in the Coliseum, but ran away with all of Oyashiro's kekkei genkai owners. Sasuke berates Oyashiro for his behaviour, only for him to retort that Sasuke, who is collecting information for others, is no different. Angered, Sasuke wins the tournament and frees all the shinobi, shocking Oyashiro. Left with no choice, Oyashiro tells Sasuke the location of Fūshin's birthplace, the Valley of Hell, which the organisation destroyed out of resentment.

In the anime, however, the circumstances of his meeting with Sasuke are different. The battle of Sasuke and Futsu is interrupted by the attack of the exploding humans. Impressed by Sasuke's performance in neutralising them, Oyashiro arranges the meeting with Orochimaru and Sasuke and provides the latter with the information about Fūshin, the Chinoike clan and their former location in the Valley of Hell. Later, when Sasuke shows up in the Coliseum once again to defeat all the shinobi and free them, Oyashiro watches him and smiles before escaping from the scene by the time Fourth Raikage and the Kumo shinobi arrived. Then, he arrives in Orochimaru's hideout and discusses the latest event with him, revealing that he's the member of Chinoike clan who slaughtered them all except his daughter, Chino. Oyashiro notes he really wanted to acquire Sasuke for himself, but later decided to use him in order to stop Chino from her pursuit of revenge for their clan, admitting he's a foolish parent, after all.

Trivia

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