Beam

Beam (ビーム) is a Shark Fiend (サメの) and a Public Safety Devil Hunter from Special Division 4.

Appearance
In his normal appearance Beam is a muscular young man with a shark's snout and fin instead of the top half of his head; he has no visible eyes. He has short, spiky black hair and very sharp teeth. He exclusively wears swimming trunks.

When he partially transforms into his devil form, his head becomes a massive shark's head with three pairs of eyes. In his full transformation, his entire body resembles a shark but with multiple sets of long fins that he uses as legs.

Personality
Beam is very eccentric. He often goes along with Denji's plans no matter how crazy they are due to having a lot of respect for the Chainsaw Devil. Even when Denji got his misinterpretation of how he should use his chainsaw abilities to enhance his mobility, Beam still went along with Denji's idea instead of correcting him.

He is shown to greatly enjoy fighting, eagerly diving into packs of zombies and eating them.

Though he was greatly afraid of having to fight against Bomb to the point of fleeing, he showed no hesitation in trying to fight back against her when cornered.

Katana Man arc
Beam is among the fighters from the Special Division 4 that are tasked with invading Akane Sawatari's hideout. He emerges from the wall belowground and dives into the pack of zombies, partially transforming his head into a shark's head and kills several of them with ease. He almost accidentally bites through the Violence Fiend but is punched back by him and reverts to his original self.

After Power drinks too much blood in the attack on Akane Sawatari's hideout and has to be taken away temporarily, Beam is assigned to be Denji's partner at his own request. He is very happy to be partnered with Denji and calls him Lord Chainsaw continuously while Makima introduces him to Denji.

Bomb Girl arc
He follows Denji around by swimming through the floor when they're out on patrol and is overjoyed when it rains. Denji tells him to stay out of sight because he'll cause a scene otherwise.

He intervenes to save Denji when Reze attacks him on their date. As soon as he jumps away with Denji he realizes that Reze is the Bomb Devil by her smell. Reze transforms and quickly catches up to him and Denji.

He tries to dodge her attacks to no avail and is blasted back by her explosions. He tries attacking her with his shark head attack but she quickly defeats him with a point-blank explosion. Before Reze can finish him off he quickly escapes with Denji as a group of civilian devil hunters briefly distract her. He takes Denji to an Anti-Devil 2nd Division Training Center and informs Aki about the Bomb Devil, stating that she is the Gun Devil's ally. When Aki questions him on how he knows this Beam claims he can't explain because Makima would kill him. Reze appears outside the building and Beam warns Aki that she's arrived.

They try to escape by car but Reze swiftly catches up to them.

After Denji is defeated by Reze, Beam and the Angel Devil restore him by feeding him blood. Beam reveals how the Chainsaw Devil used to move around in the past by using his chainsaw chain to navigate buildings. Denji makes Beam transform into his full shark form and mounts him, using his chainsaw chains like reins instead of how Beam recommended. They move in to attack Reze and the Typhoon Devil together.

They manage to wound Reze who recovers after drinking blood, and kill the Typhoon Devil after charging into his vortex and slashing him. Reze attacks from above and Beam puts Denji in his mouth to protect him, taking the brunt of the attack in exchange which incapacitates him.

After Denji dives into the water to defeat Reze, Beam later dives in after him and rescues both of them by taking them to the beach. When Reze breaks Denji's neck and leaves, Denji begs Beam to rev his engine and heal him.

International Assassins arc
Beam assists Makima and the Spider Devil in cleaning up several doll puppets controlled by Santa Claus. Makima states she'll continue to clean up the situation and orders Beam to go assist Denji which he enthusiastically agrees to.

He appears in the department store where the fight is underway and rescues Denji from being pinned by Long by bashing her in the back with his oversized shark head. He roars at her not touch 'Lord Chainsaw' and he retreats with Denji. Beam advises Denji not to use his chainsaws so that he can save up his blood, but he trips over a doll's body as they're fleeing. Denji calls him out on being clumsy but winces in pain as he stands on a nail; this triggers the Curse Devil who picks up Denji and causes him to begin bleeding profusely. Beam watches this in shock until Tolka, who had been hidden nearby, stands up and kicks Beam in the face.

Beam is knocked unconscious by Tolka's attack and is dragged to Hell alongside everybody else in the department store once Tolka's master turns him into a perfect doll and summons the Hell Devil.

When he wakes up, Beam senses the presence of the Darkness Devil and panics alongside the other fiends as it approaches them. As the Darkness Devil arrives, it cuts off Beam's arms along with the arms of every other person present.

As the Darkness Devil begins slaughtering all of the humans, fiends and devils present, Beam picks himself up and feeds blood from his stumps into Denji's mouth. He pulls on Denji's chainsaw cord to revive him and begs him to grant their wish, moments before the Darkness Devil points in his direction and cuts Beam into pieces, killing him instantly.

Control Devil arc
Beam is mentioned during the news broadcast by an interviewed woman who said she saw Denji riding him during the fight with the Typhoon Devil.

Physical Abilities
Enhanced Durability: Beam is very durable for a fiend, able to survive point-blank explosions caused by Bomb Girl multiple times and still have enough mobility to escape afterwards.

Supernatural Abilities
Intangibility: Beam has the ability to swim through solid objects, allowing him to pass through walls and the floor with ease. He doesnt seem to able to bring others with him or bring large objects through.

Shark Transformation: Beam can transform his head into an enormous shark's head with multiple eyes and great biting power. With his full transformation, Beam's entire body transforms into his Shark Devil form.

Blood Consumption: As a fiend, Beam should be able to restore his health by consuming blood.

Revival: As a Devil, Beam should revive in Hell after death. This makes him effectively immortal.

Trivia

 * His name is originated from Cherubim (ケルビム Kerubimu), an angel from the highest order of Christian angelic hierarchy along with Seraphim and Thrones.
 * Seraphim (セラフィム Serafimu) is also another follower of Chainsaw Man along with Dominion (ドミニオン Dominion) and Virtue (ヴァーチェ Vuāche) which are angels from the middle order of Christian angelic hierarchy along with Power.