Yoki

"It's not Yomi's fault... It's because Yoki is weak... Yoki will try really, really hard to be stronger... So don't cry..."

- Yoki comforts Yomi

Yoki (ヨキ) is Yomi Kasuga's oni Ayakashi. They have been together since Yomi was a little girl, and though the rest of her clan considers him a weak failure, he and Yomi are entirely devoted to each other.

Appearance
Yoki is a giant oni demon with a green body, neck length pink hair, and big bulging eyes, along with a hard shell on his back and short, purple horns on his head. His left horn holds a pledge ring, with which he shares with Yomi. He also has a long, thin tail and is capable of whipping it about at high speed, which is his primary method of attack. After his defeat at Karasumori, Yoki is only able to regenerate into a tiny, powerless version of himself, only slightly larger than a sugar cube.

Personality
Yoki has admitted that he is not very intelligent or strong, but he would do anything to make Yomi happy. The main reason he wants to get stronger is because the insults from Yomi's clan made her cry. He does not seem to mind Yomi's often pushy nature.

History
As a little girl, Yomi chose Yoki to be her oni, despite the facts that he was not very strong or smart. Though Yoki worried this was a bad decision, Yomi assured him that they would grow together and be happy. Reassured, Yoki agreed and allowed Yomi to place a contract ring around his horn. However, Yoki's lack of progress came back to haunt them: both Yomi and her family were heavily ridiculed, and Yomi closed her heart to nearly everyone but Yoki.

The Search for Greater Power
Yoki accompanies Yomi on her investigation trip to Karasumori, though he remains hidden until called upon by Yomi. She briefly reveals him while introducing herself to Tokiko Yukimura, as proof that she is an ability user from the Shadow Organization, but quickly dismisses him after a warning from Tokiko. Yoki is summoned again after Yomi has drugged and bound Yoshimori, and Tokine has fallen into her pitfall trap. Yoki eats both Madarao and Hakubi (though he notes they vanish while in his mouth). Yoshimori is stored inside of Yoki's shell. Though Yoki covers the pit with a boulder equipped with Kekkai-neutralizing charms, Tokine digs her way out. However, she has trouble keeping her Kekkai stable against Yoki's strength, especially with Yomi taunting her about her late father.

Yoshimori manages to escape his bindings and bursts out of Yoki's shell, then proceeds to destroy Yoki's leg. Yomi orders Yoki to stab Yoshimori with his tail, but Yoshimori dodges it and temporarily retreats to the woods. Yoki's leg soon regenerates faster than normal, due to Karasumori's power. Yoshimori soon faces Yoki again, destroying various body parts, only to have them regenerate. Yoshimori causes Yoki to fall, which throws Yomi from his shoulder so Tokine can capture her. But even without Yomi giving verbal commands, Yoki immediately finds and rescues her. Yoki draws on more of the site's power, growing stronger and smarter in the process. However, the power goes to his head, and he decides that Yomi is holding him back. He tosses her aside and breaks the contract ring on his horn, causing Yomi's ring to shatter as well. Yoki's new body is streamlined and built for speed, and Yoshimori has trouble pinning it down with Kekkai. He finally manages to do so, but Yoki draws on more of the site's power and starts to transform further, getting even stronger. He is interrupted by the arrival of Tokiko and Shigemori, along with Hakudo and Odo. Hakudo cuts Yoki in half, and Odo launches an enormous fireball as the finishing blow. Yomi tries to protect Yoki by running into the fireball's path, but recognizing the danger, Yoki pushes Yomi away to protect her instead. Yoki's body is destroyed in the explosion, but Yoshimori manages to save a tiny portion of Yoki's horn and gives it to Yomi. Surprisingly, Yoki regenerates into a tiny, powerless version of himself from the horn, and has returned to his senses.

Natural State
Limited Phasing: Yoki can phase parts of this body through solid matter without disturbing it, shown when he phases his hand through the street outside of the Yukimura Home. He can also store people and objects inside of his shell.

Fast Tail Movement: Yoki has a very long, fast tail that he uses like a whip or a spear, and it can be very hard to dodge.

Oni Strength: Though Yoki is not very strong for an oni, his enormous size still allows him to put a great deal of force behind his blows. Regeneration: Yoki has the natural ability to regenerate his body after suffering damage, including lost limbs and the majority of his body at once, if necessary. The power of Karasumori temporarily boosts this ability, so that he recovers in seconds.

Multiple Tails: While normally Yoki has only one tail, due to the influence of Karasumori's power, he was able to grow multiple tails.

Boosted State
Increased Speed and Compact Body: Yoki judges that his main weakness is lack of speed, and uses the power of Karasumori to streamline his body so that speed becomes his greatest strength.

Trivia

 * Yoki is the first Ayakashi seen destroying both Madarao and Hakubi, though it's implied in the manga that Madarao has been killed by Ayakashi multiple times since Yoshimori has known him.
 * Yoki's name (ヨキ) means expected.