Enishi Yukishiro is the younger brother of Tomoe Yukishiro and the primary antagonist of the final story arc of the Rurouni Kenshin series, also appearing in the Trust & Betrayal OVA. Born in May 1855, his mother died shortly after his birth, leaving his sister Tomoe to raise him as a parental figure. As a young boy, he was largely indifferent to the world around him, with his deep love and respect for Tomoe being his sole emotional anchor. His initial animosity towards Himura Kenshin, then known as the Hitokiri Battousai, stemmed from Kenshin killing Tomoe's fiancé, Kiyosato Akira, an act that devastated his sister. Enishi was only nine or ten years old when he ran away from home to join the Shogunate agents tracking Kenshin, believing he was helping Tomoe exact her revenge. It was during this time that he witnessed the pivotal event of his life: Kenshin accidentally killing Tomoe in a final attack against a spy from the Yaminobu. The trauma of watching his sister die by Kenshin's hand caused his black hair to turn stark white from grief and shock. After cursing Kenshin at the site of Tomoe's grave, Enishi fled a now-changed Japan for Shanghai, leaving behind a country built by the revolutionaries and the man who killed his sister.

Enishi's personality is defined entirely by the trauma of Tomoe's death. For the decade following the incident, time effectively stopped for him; his existence became a living hell driven by a singular, obsessive desire for revenge. He outwardly presents a facade of polite calm and strategic thinking, which he uses to manipulate his subordinates and gain the trust of others. Beneath this veneer lies a deeply unstable, short-tempered, and ruthlessly vengeful individual. His hatred for Kenshin is absolute; he does not simply wish to kill him, but to make him experience the exact same "living hell" of losing the person he cares for most. Enishi's commitment to this goal is fanatical. He believes he constantly sees the image of his sister smiling, interpreting this hallucination as her approval and even a demand for revenge, which he calls jinchū, or "judgment from man". Despite his cruelty, a softer side exists only in his communication with the memory of his dead sister. After his defeat and the shattering of his vengeful spirit, he falls into a state of hopelessness and depression similar to what Kenshin once experienced.

Enishi's motivation is pure, all-consuming vengeance. He deliberately constructs an elaborate plan not just to defeat Kenshin physically, but to psychologically devastate him. His goal is to carry out jinchū by taking away Kamiya Kaoru, the woman Kenshin loves, mirroring what he believes Kenshin did to him when Tomoe was killed. He organizes a group of six powerful warriors and specialists, known as the Six Comrades, to assist him in systematically attacking Kenshin's friends and allies. His ultimate act of cruelty is using the corpse artist Gein to create a lifelike doll of Kaoru, making it appear as though he has driven his sword through her heart, thereby plunging Kenshin into a catatonic state of despair. Enishi's own trauma is so profound that, despite his rage, his subconscious cannot allow him to directly harm Kaoru because she reminds him of Tomoe, a psychological block that forces him to rely on tricks like the doll.

Enishi's role in the story is that of a dark mirror to Kenshin. He is the living embodiment of the consequences of Kenshin's past as an assassin. Unlike previous antagonists like Shishio Makoto, who represented a political or ideological threat, Enishi's challenge is deeply personal and psychological. The author Nobuhiro Watsuki intentionally designed Enishi as a "depressive type" villain, one who is "falling deeper and deeper," in contrast to the "manic" Shishio. Their conflict is not about ideals but about grief, guilt, and the destruction left in the wake of violence. Enishi's fighting style, Watōjutsu, is specifically noted to perfectly counter many of the techniques of Kenshin's Hiten Mitsurugi-ryū, making him a physical match as well as an emotional one.

Key relationships define Enishi's entire being. His bond with his sister Tomoe is paramount. She was his mother, sister, and the only person he ever truly cared about protecting. His father, known only as "Geezer," is an old man living in a fallen village whom Enishi does not initially recognize, their family having been sundered. His relationship with Kenshin is one of pure antagonism. Enishi refers to him as his brother-in-law but despises him wholeheartedly, believing he intentionally murdered Tomoe. Kamiya Kaoru serves as the target of his jinchū and, ironically, becomes the person who ultimately hands him Tomoe's diary, revealing his sister's true feelings for Kenshin, which begins to crack his worldview. He holds a dismissive and strained relationship with his subordinate, Woo Heishin, viewing him as a tool rather than an ally.

Enishi's character development is a tragic arc from trauma to vengeance and finally to broken realization. After his plan fails and Kenshin defeats him, his spirit is completely shattered when the illusory image of his smiling sister finally disappears from his mind. He is arrested but later escapes to find himself in the same fallen village where Kenshin had once recovered. There, his father tells him to rest and that he will one day find new purpose and recover, just as Kenshin had before him. This suggests a potential, if uncertain, path toward atonement rather than a simple death for the villain.

In terms of abilities, Enishi is a prodigiously skilled swordsman and self-taught master of Watōjutsu, a style blending the speed and slashing power of Japanese kenjutsu with the strength and flexibility of Chinese sword arts. He wields a Watō, a Chinese-made Japanese tachi. His style is purely offensive, relying on overwhelming power and speed while disregarding defense in favor of counter-attacks. His signature ability is the "Frenzied Nerves," a state where the nerves throughout his body bulge, granting him dramatically enhanced senses, speed, strength, and reaction time. This allows him to perceive and counter attacks before they are fully executed. However, this is a double-edged sword, as his heightened senses also magnify any pain he receives, making him incredibly vulnerable to physical strikes. Out of all the opponents Kenshin faces, Enishi is the only one to fully block the Kuzu Ryū Sen and even counter the ultimate Amakakeru Ryū no Hirameki, proving himself to be one of the most formidable and technically skilled adversaries in the series.