Fuji

is a first-year at Ishiyama High School who is formerly from Shinkyōku High School.

Appearance
Fuji is a tall and well-built young man with spiky hair that falls to his shoulders. His usual attire consists of a long-sleeved dark shirt and light-colored pants, complete with a pair of light shoes.

When his silhouette was first shown, he appeared to be wearing a dark jacket with a chin-length collar, which also appeared to be worn closed.

Personality
Fuji is a calm and carefree young man. He is the type of person who spends much of his time on the Internet and rarely interacts with other people. He claims to be a recluse and states that he isn't the type to be won over by emotions. He also seems to dislike loud noises, as he was annoyed at the noise created by the other delinquents of Ishiyama.

Fuji, however, does love to fight strong opponents, as he wanted to fight Oga with Beel's powers and at his best condition, stating that it would be more fun doing so.

History
Fuji was a former pupil of Zenjūrō Saotome and learned spells under his tutelage.

In the past, Fuji attended Shinkyōku High School, where he eventually gained recognition as the "strongest rookie" ever. However, he eventually decided to attend Ishiyama High School in the new semester following its second reconstruction.

Sometime before attending Ishiyama, Fuji came into contact with the Solomon Company. He later formed a contract with Satan, one of the Seven Deadly Sins, and was labeled by the organization as one of the "Six Omens of Slaughter", notably being one of three who were able to handle them.

Return to Ishiyama High School Arc
Fuji first appears in Oga's house when the latter just came back from America. When Oga attempts to talk to his mother and Misaki, Fuji, sitting on a couch, notes that they won't respond as they were already turned into stone. Commenting that the tea Misaki made sucks, Fuji stands up and introduces himself to Oga. He then apologizes to Oga as he tells him that he is a recluse and that he left his room just to see Oga. He then adds that everyone was loud that it pissed him off so he turned all of Ishiyama to stone. Enraged by the fact that his mother and sister were turned into stone, Oga attempts to attack him with a Zebul Blast but suddenly realizes that he can't as Beel isn't with him anymore. Fuji, commenting on how boring and weak Oga's punch is, punches Oga in the face, sending him crashing through the wall and through several houses. He then inquires Oga if he went to the Solomon Company and tells him that a reaper told him that his enemy Beelzebub has just awakened. Telling Oga that he was looking forward to their fight, he then expresses his disappointment on how Oga quickly became weak just after separating from Beel. He then tells Oga to bring Beel back or if he would like to die without a fight.

Suddenly Yōhei Nasu arrives and kicks him in the face, telling him that he was the one who was going to die. Fuji, not even flinching to the kick, is suddenly attacked by Shinobu Takamiya who crashes a car down on him. After a small greeting from one another, Takamiya suddenly jumps off the car as Fuji notices Kankurō Akahoshi preparing a fiery attack on him. The attack hits and the car on Fuji is engulfed by the flames resulting in a very fiery explosion. However the attack didn't even affect him in the least as he just walks out of the explosion basically unscathed. He is then confronted by Takamiya and Nasu as the two Spell Masters prepare to fight him. He then asks the two if he needs to beat them in order for him to pass and if they are now working for Oga. He then tells them that there is no point in fighting for Oga anymore, as without Beel's power, he's just a regular human. Suddenly he gets pulled in by Lucifer's power as Takamiya asks him why he is still chasing Oga. He is then punched in the face by Takamiya, momentarily pushing him back, however Fuji quickly regains his posture and answers him that he is chasing Oga as fighting him will still be better than fighting them. He then attacks them, causing a large explosion that devastates the area.

As the explosion settles down, Takamiya and Nasu's bodies are singed and slowly turn into stone. He then notices the barrier machine and immediately tries to go to its location. However he is quickly grabbed by the leg by Nasu, telling him that they're not done yet. He then cuts off Nasu's already petrified arm but he is again grabbed by Nasu and Takamiya. He then tells them that they don't make any sense and asks them why they would go so far just to let Oga escape. He then escapes from their hold and immediately goes to where Akahoshi is. He asks Akahoshi what are they to Oga, as they are not so close to Oga to be called a team with him and adds that since he is a recluse, they won't win him over with emotions. He tries to attack but is stopped by Himekawa who tells him that he will never beat Oga because of this. As Himekawa gets turned into stone, the machine activates, causing the link between him and Satan to be cut off. Akahoshi, the only one left who can protect the machine, sets his fists ablaze and punches Fuji, who is then pushed back.

Powers & Abilities
Spell Master (紋章使い (スペルマスター), Superu Masutā): Fuji is a highly skilled and well-experienced Spell Master, according to Saotome. Saotome stated that he and Takamiya were worlds above Oga in terms of abilities and experience. He is also capable of easily defeating both Takamiya and Nasu, the other two members of the Three Beasts and both highly skilled Spell Masters, in less than 20 seconds something that made Himekawa note that Fuji is a true beast. This demonstration shows that his skills is perhaps second only to Saotome himself who is the strongest human character and spell master in the series. Though as the two never actually fought it's unknown who is truly stronger. Fuji's overall abilities are as such that all of the other Killer Six Elements and Oga's friends had to ally together to combat against Fuji and even then they could not defeat him at all. Master Hand-to-Hand Combatant: Being the most powerful member of the Killer Six Elements, Fuji is an extremely powerful young man which even led him to gain the title as "the strongest rookie". Fuji's strength allowed to fight against two members of the Killer Six Elements such as Takamiya and Nasu simultaneously and overpowered them.
 * Petrification: Through his contract with Satan, Fuji is able to petrify others thus turning them into stone statues. When he recalls the power used in the petrification, they return to normal.
 * Petrification Explosion: Instead of a normal energy blast like most other demon contractors and spell masters, Fuji creates an explosion of demon energy that annihilated a portion of the neighborhood while petrifying both Takamiya and Nasu simultaneously.
 * Demon Fusion: When fighting against Oga and Baby Beel seriously, Fuji and Satan proceeded to fuse together to use the demon's full powers in the human world. This fusion causes Fuji to take on the appearance of a fallen angel/demon hybrid. During the fusion if they are agitated, Satan's personality starts to take over. After being defeated by Oga's Zebul Finisher, the fusion is dispelled.
 * Flight: As Fuji gains a pair of black wings in this form, he is capable of high-speed flight.
 * Immense Demonic Power: While fused with Satan, Fuji can emit a huge amount of demon power that allowed him to compete against Oga's Super Saiyan Switch even after expending a great deal of power petrifying everyone else.
 * Enhanced Durability: While fused with Satan, Fuji's durability increases to where he is capable of enduring attacks from Oga in his Super Saiyan Switch and continue to counterattack.
 * Energy Blast: For a final attack, Fuji and Satan regather the demonic power used in their petrification, to gather it around for an enormous energy blast that was able to compete against Oga's Zebul Finisher in power that the latter had to absorb the power of the humans and demons aligned to him to overpower Fuji and Satan's attack.

Immense Strength: He is capable of defeating Oga (albeit without Beel) and send him crashing through several houses with only one punch. He easily held up a car thrown to him by Nasu with just one arm while the bumper of the car was bent when it crashed into him. Fuji was able capable of flicking aside one of Laymia's, a Pillar Baron and 2nd in command of the 34th Pillar Division, energy attack with his finger alone.

Immense Durability: Fuji is durable enough to resist attacks coming from both Nasu and Takamiya at the same time with little damage. This was shown when he was unharmed after having a car thrown on atop of him by Nasu, being in the center of the explosion of its destruction caused by Takamiya and taking Takamiya's punch enhanced by Lucifer's gravitational pull. This led Nasu to question if Fuji was a human and Takamiya to declare him as a a monster.

Zenjūrō Saotome
Sometime during his childhood, Fuji learned spells from Saotome. Not much is known about their relationship, but Saotome is shown to have enough confidence in Fuji's skill to warn Oga about not fighting him or Takamiya.

Quotes

 * (To Tatsumi Oga) "Sorry 'bout this, Tatsumi Oga. I'm a recluse. Its been a while since I went outside, but I left my room just to see you. I just don't have the courage to talk to people. I've been on the Internet this entire time, after all. But when that wasn't enough anymore I decided to go to school. But I couldn't find you. And everyone else was loud as hell...it pissed me off, so I turned them all to stone...only in Ishiyama, though."
 * (To Yōhei Nasu and Shinobu Takamiya) "You're not making any sense. Why would you go this far just to let Oga escape?"
 * (To Kankurō Akahoshi about his relationship with Oga) "What the hell are you guys to him? You're not so close to him that you can be called a team, right? Since I'm a recluse, you won't win me over with emotions." 
 * (To Tatsumi Oga in regards to the fate of Akahoshi and the others) "Turned to stone, of course. All of them. That last one was a damn pain though. But it was so funny, every last one of them. Kept saying, Oga...Oga...like it was a chant. I wished they would've considered me since I had to keep hearing it."