Sekiei

is a fabrication, that was created to serve Kū and to lead the Akuta in order fulfil Ōnoki's desire to protect peace within Iwagakure and the shinobi world.

Personality
Sekiei is a very childish individual. He shows a very light-hearted nature, as he enjoys drawing randomly and is very open with his thoughts. Ironically, while looking down on humans as weaker, he is nonetheless very fascinated by their emotional nature and group interactions.

Appearance
Sekiei is a young man with brown, bowl-cut hair and pale skin. He has large, green, pupilless eyes and the lower half of his face is concealed by bandages. He wears a purple tunic over a black bodysuit, his hands also being covered by bandages.

Abilities
Being created with special powers and jutsu, Sekiei was implanted with Explosive Clay, allowing him to simultaneously use Earth and Lightning Release to use Explosion Release. Utilising the kekkei genkai to use C1, Sekiei can create a variety of clay insects that explode.

Mitsuki's Disappearance Arc
Sekiei first appears at the entrance to Konohagakure, supporting Kokuyō as he attacks Saō and Uō. He leaves both men incapacitated before fleeing with Mitsuki. When the genjutsu on Yurito was broken, Sekiei's C1 detonated in an attempt to kill him, but Yurito survived, though was left in a critical condition. On their way back to the Land of Earth, Sekiei took an open liking towards Mitsuki as an artificial human. He began talking about how Mitsuki's being would help in advancing their goal, only to be interrupted by Kokuyō, who didn't trust Mitsuki with such information. As they approached the Land of Stone's border, Kokuyō noticed that they were being pursued by Konoha-nin. Sekiei was sent ahead with Mitsuki while Kokuyō engaged the pursuers.

When they learned that two Konoha-nin made it past Kokuyō, Sekiei left Mitsuki with the two Akuta while he faced the enemies. Sekiei was intrigued by the Boruto Uzumaki and Sarada Uchiha's fixation on retrieving their "friend" Mitsuki. Despite this, he quickly went to work to kill them. As his Explosive Clay proved to powerful for the Konoha-nin, Boruto summoned Garaga to aid. While the giant snake initially refused to help, ultimately began attacking Sekiei on the grounds of proving his might. Sekiei prepared a counter-attack, by his body suddenly gave out in strength. Luckily, he was saved by the timely arrival of Mitsuki. Mitsuki then made his intentions clear joining the artificial men by striking Boruto hard with his Lightning Release, thus earning Kokuyō's full trust as they departed from Boruto and Sarada.

Later, as Sekiei's body began breaking down again, Kokuyō left Mitsuki to look over Sekiei while he returned to base for help. As they passed the time with Mitsuki telling Sekiei more about human nature and his life in Konohagakure, he suddenly ensnared Mitsuki with one of his clay insects. He revealed he was aware of Mitsuki feigning killing the guard from earlier and leaving behind a snake. Mitsuki insisted that he merely left a message saying he make the personal choice freely leave Konohagakure. Accepting that Mitsuki really had no ulterior motive besides learning who he really is, Sekiei decided to hide Mitsuki's secret message as a sign of friendship. Soon afterwards, Sekiei's fellow artificial humans arrived and partially treated his condition, stabilising him enough to get him back to the base while Sekiei vouched for Mitsuki's trustworthiness.

After fully recovering and returning to their headquarters, Sekiei showed Mitsuki around, including Mitsuki's room his own. Inside Sekiei's, there were various drawings he made of people he cared about, including Mitsuki. Mitsuki was then brought before a scientist to analyse his unique body. During which, they found Cursed Seal on Mitsuki's heart. When Kirara's body began weakening, it caused her genjutsu on the village officials to end. Realising that they had to take drastic measure to keep their work secret from the outside world, Kū launched a hostile takeover. Once succeeding, the artificial humans began growing irritable at Kū's refusal to try a human heart transplant on them, which could likely save their lives, on the grounds that hey did not yet have Ōnoki's permission. They were then tasked with finding Ōnoki.

When Ōnoki was found but refused to go through with the transplant, Kū decided to take charge and subdue the elder. Sekiei was then very eager to feel more human once getting a heart. Later, Sekiei's body began to break down once more and the doctor tended to Sekiei's deterioration. Sekiei asked the doctor how their lives would be after receiving their hearts. After receiving the doctor's answer, Sekiei only wanted to protect his friends while not wanting to be strong. Sekiei informed Mitsuki that he found out Kakō and Kokuyō had been defeated by the Konoha genin. He asked Mitsuki how that would change once he received his heart, only for Mitsuki to answer that having a heart doesn't make one human.

After Sekiei's condition was treated, Sekiei and Mitsuki went to meet Kū while delivering a completed artificial heart. Sekiei witnessed Mitsuki's betrayal after giving Kū the heart, revealed to be disguised snakes, leaving Sekiei enraged.

Trivia

 * means "quartz".