Kouki Samejima

Kouki Samejima is a human and a Ancient Gear possessor. He is a renowned school delinquent from Ryoukou High School.

Appearance
Samejima is a handsome young man with spiked up dyed brown hair and gray eyes.

History
Kouki is one of the few students who missed his school trip thus avoiding being captured by the Utsusemi Agency.

Volume 1
Kouki is first mentioned by Natsume to Tobio as an ally. He is first shown in a deserted departmental store where he goes to take out some Utsusemi. He is found by Tobio, who was searching for him along with Natsume, Damian and Lavinia. As Tobio follows him, he asks Tobio the reason for his presence, to which Tobio replies that he's trying to rescue their former classmates from the Utsusemi Agency. They introduce themselves to each other and make their way to the fifth floor, where they are confronted by Kazuhisa Doumon who overwhelms and subdues the both of them with a powerful clay doll. Kazuhisa tries to kill one of Tobio's friends in a, particularly cruel manner, making Kouki express rage. Kouki then watches one as Tobio's power increases and forces Kazuhisa back. They are subsequently joined by Natsume, Damian and Lavinia, and decide to make their way to the meeting with the Governor General. At the meeting, the Governor-General further explains the current situation to them and also their Ancient Gears.

Later on, the team decides to visit the house of Sae in relation to the current situation. Upon their arrival there, they split into groups of two with Kouki being with Natsume and Damian. Soon after, they find out that they have been ambushed by the enemy, with Tobio telling him, Natsume and Damian to escape. As they run away from the premises and reach a deserted factory, Kouki is confronted by an Utsusemi taking the form of his close friend's little sister. Letting his guard down, he is impaled and suffers a serious injury. Kazuhisa reveals himself as the instigator of the incident, appearing with Kouki's friend. His Ancient Gear, Byakusa, performs medical treatment on him. As the situation looks bleak, he tells Natsume and Damian to escape but their Ancient Gears suddenly evolve and defeat Kazuhisa, who tries to escape, only to be obstructed by Vali and Asriel. As Vali attempts to handle Kazuhisa, Kouki tells him to wait and punches Kazuhisa himself, collapsing afterward due to his injury. He is subsequently teleported by Vali to the Grigori institute along with Byakusa.

Ten days after the incident, it is revealed that he has been registered at a special school under the Grigori called Nephilim, along with the rest of the team.

Volume 2
Two months later, Kouki is shown making his way to Tobio's room along with Damian, Lavinia, Vali, Asriel, and Sae, where they see him in bed with Natsume, causing an awkward situation to manifest. As the misunderstanding is cleared up over breakfast, Azazel appears and takes them to Nephilim, where he introduces them to Baraqiel, who is to be their teacher.

Half a month later, he is seen at Nephilim, completing a training course with Tobio and Damian and discussing with them. Baraqiel then places him, Tobio and Damian in a sparring match against Vali, which they lose, much to their frustration. The following Saturday, he goes along with the rest of the team into town. As they rest at a park downtown, they are suddenly joined by an pair of a bespectacled and a ruffian looking young men who introduces themselves as Seiryuu Kushihashi and Andreas Hoffman. Quizzed on his intentions, Seiryuu replies in a vague manner, making Kouki irritated as he summons Byakusa. He fights against Seiryuu and Andreas along with Tobio and Damian, but the match is interrupted by the arrival of Baraqiel, Vali, Asriel, and Suzaku Himejima, who asks for a meeting.

At the meeting, Suzaku apologizes for the incident with the Utsusemi Agency and informs them that they are searching for their former classmates, who are being chased by the Utsusemi Agency and the Wizards of Oz. She then asks for an alliance, much to the surprise of himself and some others. They agree to the alliance, resolving to rescue their former classmates. As they prepare and head towards the location, Baraqiel warns them about the abilities of their potential enemies and Lavinia tells the team about her past, leading them to express their support for her. As they reach closer to the location, Sae raises an alarm, causing Baraqiel to investigate ahead. He finds Shigune Nanadare, one of their classmates, along with her Ancient Gear. She warns them to escape, just as they are confronted by a strange stone statue. Soon after Baraqiel cautious the team to close their eyes, the statue releases an intense light that is revealed to be capable of causing blindness. A man soon reveals himself, expressing his desire to make them blind. Kouki attacks the statue along with Tobio and Damian, as the man is forced to retreat. Shigune then tells them that Koga and Lily, their other classmates, are fighting alone in the village.

Following that, they head towards the village. After they feel a powerful aura determined to be that of Kokabiel, Baraqiel decides to pursue Kokabiel alone and gives instructions to the team. After they reach the location, they discover Koga and Lily who are surrounded by gruesome and dismembered corpses, which disgusts the team. Koga and Lily acknowledges Kouki and the rest of the Ryoukou students. They notice Augusta and several other magicians, who have surrounded them. As Lavinia pursues Augusta alone with the approval of the Ryoukou students, Kouki tells Tobio, Sae, Natsume and Shigune to follow Lavinia while he deals with the other magicians along with Damian, Vali, Koga and Lily.

Later, Kouki and others are informed that Augusta managed to possess Lavinia's body. They receive instructions from Azazel on how to combat Augusta. Kouki then helps the rest of the team to defeat Augusta and safely retrieve Lavinia. Ten days later, the team is shown together in a hospital as they express their support for Lavinia in her future goal.

Power and Abilities
Expert Combatant: Kouki is shown to be an adept fighter, being able to use the transformed Byakusa proficiently.

Expert Spearman: With Byakusa's tail spear, Kouki could hold his own against Utsusemi and defeat them, being skilled enough to coordinate their attacks and target their weak points. With continuous training in the Nephilim Institute, Kouki could hold his own against Seiryuu, Andreas and Byakko.

Enhanced Speed: In Volume 2, following his training at the Grigori, Kouki's speed has improved as he can shrink the distance between him and Seiryuu.

Equipment
Unnamed Ancient Gear: Kouki's Ancient Gear which takes the form of a white cat whom he has named Byakusa ( White Sand). It is one of the Four Fiends and Friends Ancient Gears bearing the spirit of . It also has the power to create a large amount of electricity. It is capable of transforming into a spear for Kouki's use. As of Volume 2, Samejima can manifest electricity around the spear.
 * True Form: It takes the form of an enormous tiger with several tails and with electricity around it. In this form, he can use electricity to attack and his several tails.
 * Healing: Byakusa can also heal Kouki of grievous injuries by transplanting its own flesh into his wounds, assimilating its own flesh into Kouki at a cellular level, allowing Kouki to survived being impaled through the chest.

Trivia

 * His first name Kouki (綱生) means "Unrefined Class".
 * His surname Samejima (鮫島) means "Shark Island".