Yuudai Saejima

Yuudai Saejima (冴島さえじま 雄大ゆうだい) was Minoru and Akane's former high school classmate at Sakurazaka High School. Following the fall of Japan to Magical Beasts, he became the Vice-Commander of the Knights in the human settlement of Messiah and mole for The Alliance.

Appearance
Yuudai was a young adult with short black hair and facial hair whilst wearing a black shirt with a necklace under a Sakurazaka Senior High uniform as his Messiah uniform. It should be noted that he was often referred to as a gorilla due his bulky physique and expertise on Judo. He was also considered handsome by many students at his high school.

Personality
Not much was known about Yuudai's personality when he was a student. However, as a Vice Commander for the Messiah, he was a blunt man who would abuse his position in attempt to force Akane into a relationship and would even go as far as to blackmail her to do as he says.

Background
Former student of Sakurazaka High School and classmate of Minoru and Akane, he was considered by many fellow students handsome and was popular except Akane. He was a member of the school's Judo club and competed in the nationals before Japan was invaded by magical beasts.

The Birth of the First Knight
Not much details were given of his whereabouts during the birth of the First Knight. However, he was aware of the identity and would use it as leverage against her when possible. Sometime after the destruction of Arcadia, Yuudai would rose up into the ranks of the Messiah to Vice Commander and would eventually be bribed into the Alliance as their mole by Yuuka.

Reunion
After Akane took Minoru into her care, Yuudai introduced himself and chastised her for taking him in and suggested that they should've left him for dead. The conversation between the two grew tense after the suggestion as the Vice Commander reminded her of their positions within the ranks of Messiah and reached a breaking halt when Akane protected Minoru from him. However, this enraged Yuudai as he revealed his knowledge of the First Knight before leaving the two much to her denial.

Sometime after, Yuudai would break into Minoru's room and accused him of being a spy. He attempted to "interrogate" him until Akane stepped in to stop him. Yuudai leaves the room and reminded Akane that they had an emergency meeting later. During the meeting, Yuudai was shocked to see photographs of dozens of mangled magical beasts and demanded to know whose responsible of such feats. Initially, Haitani deducted that the First Knight was responsible but concluded that there was another Knight of her caliber much to their relief.

During a magical beast stampede, the Messiah Knights were overwhelmed as Akane was almost killed when Shadow (who took on the alias "Black Knight") saved her alongside the group much to Yuudai's ire and suspicion of his affiliation. Yuudai would meet his end when he slipped off to the back of Sakurazaka Senior High to meet up with his Yuuka regarding intel she gave him. He was caught off guard and killed when the double agent shoot him multiple times before asking "why?".

Skills and Abilities
Yuudai was noted to be an expert at Judo as Minoru recalled in his past life that he was the in the school's Judo club and even competed in the nationals before the magical beasts invaded Japan. He was also a proficient fighter as he could use magic. However, his magic is considered dismal under Other World's standards when compared to members of Shadow Garden, the Crimson Order, and even Akane as demonstrated in his struggle against a magical beast stampee.

Akane Nishino
Akane's former classmate, she saw no appeal and despised him for how he looked at her sexually since their time as students. However, this does not stop Yuudai as he often tried to force her into a relationship to no avail. Whenever the two have argued or enraged, he often abused his position and blackmailed her under the threat of having her recall memories as the First Knight much to her anguish.

Due to their poor relationship, Akane was the first person to be accused when Yuudai was discovered dead after fending off a magical beast stampee.

Yuuka
Fellow double-agent for the Alliance, Yuudai was bribed into their side as their mole in the Messiah until Yuuka murdered him after fending off an magical beast stampede and after she got what she needed. She would also exploit Yuudai's death in attempt to frame Akane as a murderer.

Haitani
Much of their interactions are unknown during Shadow and Beta's time on Earth. However since Haitani was the Commander of the Knights of Messiah, Yuudai would be outranked and would follow orders under him.

Akira Nishino
Scientist for the Messiah and Akane's brother, Akira was unaware of either Yuuka and Yuudai's antics until his death.

Minoru Kagenō / The Black Knight
Former classmate of his late incarnation, Minoru was able to recall Yuudai in his past life as he was affectionally referred to as a gorilla and expertise on Judo. When Akane took Minoru in under her care, Yuudai tried to leave him in a monster nest to eaten by monsters until Akane protected him. Yuudai also tried to use Minoru as a scapegoat when he accused him of being a spy before Akane to stepped in to protect him once more.

As the Black Knight, Yuudai's view of him would contrast much like Iris'. He was initially shocked to learn of his existence during the meeting but was enraged and suspicious the Knight when he effortlessly saved Akane and kill off the remaining stampee.

Natsume
Although the two has never interacted, Yuudai has acknowledged her potential as a possible knight within their ranks and suggested that Akane should've simply taken her instead of the both of them in much to her ire.

Trivia

 * Yuudai was one of the only known students of Sakurazaka High School before the invasion. The others would be Akane and Minoru.