Know

Know (ノー Nō) or "The Know" (THE・ノー THE Nō), also known as "Fake Fire-breathing Bug"(偽火吹き蟲 Nise Hifuki Mushi), was an arsonist responsible for the Shakuzawa Building fire, Suzuka Shinoyama's death, the attack on the Shinoyama estate two years later, and committed his attacks in the name and style of the arsonist Fire-breathing Bug. After his arrest following the Shinoyama estate arson, he was killed en route to a police station by the real Bug.

Before Know's death, those with the Evil Eye would have been able to see the faceless spirits of the Shinoyama bodyguard and maid whose faces he stole and identities he impersonated.

Appearance
Know was a bald man with a burn scar stretching across his nose and left cheek. He wore at least two highly proficient disguises when posing as at least two servants in the Shinoyama manor: a brunet, mustachioed male bodyguard in a steward's uniform and a light-haired woman in a maid's outfit.

Personality
Know was obsessed with the act of burning, taking more enjoyment in burning people than he did objects. He was meticulous and dedicated when preparing his arson sites, willing to spend over a year setting up a single job.

Background
Two years before the start of the manga, Know burns a bodyguard of the Shinoyama Clan to death and steals the man's face. Thus disguised as the bodyguard, he subsequently meets with the husband of Rozan Shinoyama's niece on the Shinoyama estate grounds to discuss a job the man has for him—or rather, Fire-breathing Bug, whom the man believes him to be: to burn the manor and the Shinoyamas with it.

Given the manor's size, Know estimates he will need two years to prepare for the job; he also suggests blaming the eventual fire on the twins Kazuki and Shizuki Shinoyama if the goal is to make the fire look like an accident. A moment later, he detects an eavesdropper—Suzuka Shinoyama—in the bushes and smiles at the prospect of burning some "succulent meat" as Suzuka races away in a bid to warn her family of the arson plot. She cannot do so; seconds after she enters the boiler room, Know causes the boiler room to burst into flames.

The boiler room explosion is deemed an accident. Know can spend the next two years preparing the manor for his arson plot at his leisure, posing as the bodyguard. Toward the end of those two years, he also commits the Shakuzawa Building arson which the media attributes to Fire-breathing Bug. At some point, he also scouts out Youtoukorou, where he recognizes Misaki Sakimiya as the assassin killer Zaki.

Not long after the Shakuzawa fire, Know and several other bodyguards escort the Shinoyama twins to the abandoned building where Rozan's missing son Polka Shinoyama lives. The twins proceed to entreat with "Polka" (who is possessed by the Corpse God) while his friends Takumi Kuruya and Misaki look on; of the bodyguards, Know is the only one who keeps an eye on Misaki the whole time. The same day, the husband and Know discuss the execution of their plan.

The next day, "Polka" and "Polka's" friend Misaki arrive at the manor for lunch; as they enter the manor, the husband calls Know's phone to inform him of the additional targets and request the job be carried out regardless as previously discussed.

Once lunch is concluded, Know follows Kazuki and Shizuki to their bedroom and calls the husband en route to ask if he is fine with him beginning the job. The husband confirms he is, as he is already well away from the manor. With that, Know sets his plan into motion. First, he sets off a large explosion heard throughout the manor; then, he bursts into the twins' room and urges them to follow him to safety. The twins follow him until they reach a descending staircase, which Know claims leads to an escape route. Kazuki objects that no such route exists, but Know insists it does—he spent two years building it.

The twins shrink back as Know advances toward them with sparking gloves, all three unaware of Suzuka's spirit futilely trying to stop Know in his tracks. Where Suzuka fails, a newly arrived Misaki succeeds with a flying kick to Know's cheek, sending him crashing to the floor.

Know's face slips off as he stands, and he subsequently removes his wig rather than trying to maintain the disguise. Though he claims he had only planned to have the twins "for a snack today," he decides to have a feast now that Misaki has arrived. Undeterred, Misaki tells the twins to run. Once the twins are gone, Know identifies Misaki as the assassin-killer Zaki, and Misaki remarks that Know was the only person keeping an eye on her at Polka's building—hence why she was keeping an eye on him this time.

The two fight, with Misaki refusing to answer Know's questions about what she is doing with the Shinoyamas. She instead comments that she thought Know would immediately pursue the twins when they ran, but Know—who presumed Misaki would have attacked him from behind in such a case—retorts that he did not give chase because neither she nor the twins would be escaping. A new sea of flames envelops the room, which Know promptly abandons.

By the time or after Know reaches the outside, he has changed into a second disguise: that of a female maid whose face he stole at an unknown time. While the other servants crowd around the successfully escaped twins, Know decides to sneak away and return to burn the house down another day. He is immediately intercepted by "Polka," who observes that Know has made "quite the pair of enemies"—i.e., the bodyguard and maid, whose faceless spirits have followed Know the entire time.

Know twists around in a panic, his voice reverting to his own, but Misaki kicks his cheek and sends him crashing into the wall for the second time that day. Know staggers to his feet and rummages through his pocket for one of his special gloves, which he puts on while "Polka" talks about killing him. Afraid of the pressure rolling of 'the kid', Know remarks that "Polka" reminds him of when he woke to his fire powers and used his glove to set off another explosion.

The blast creates a wall of flames that separates "Polka" from Know, who gloats until Lemmings lunges through a hole in the wall behind him and smashes his head to the ground.

With Know incapacitated, Lemmings carries his body off the estate and somehow or another ensures the police arrest Know. Know soon finds himself handcuffed and in the back of a police car, a tad ruffled but not overly concerned due to the gunpowder sitting in his stomach. Concern swiftly seizes him at the sight of the words "This world is a buggy program" scorching into the car's ceiling—the purported motto of the real Fire-breathing Bug—, and he immediately panics, begging the three police officers to let him out.

The police car screeches to a halt. In seconds, the police officers cease trying to quiet Know down and appear to stare at him eerily. Know is accused of being a "sham, phony bug" who needs to be "put down," with that, he appears to combust spontaneously. All of the police officers—evidently 'normal' once more—react with shock; the driver manages to escape the vehicle and watches it burst into flames with Know still inside.

Later that day, the news reports that two police cars went up in flames and that the suspect—a man suspected of arson, name unreleased—being transported has been confirmed dead.

Trivia

 * When Lemmings incapacitates Know, the bodyguard's spirit 'dies' from fright upon seeing Lemmings; the maid, however, physically reclaims her face from Know and forms a contract with the Corpse God.
 * Fire-breathing Bug's calling card motto always begins with "this world is a buggy program," but what the media has not been told is that the phrase is always the first of two parts. With Know's knowledge of Fire-breathing Bug limited to what is published in the media, he has only ever left "This world is a buggy program" at his arson sites. This detail allows the police to recognize his arson attacks as copycats rather than arson committed by the real Bug.
 * The husband later claims to Takeru Shinoyama that he only sanctioned the arson because a "Fire-breathing Bug" threatened him. Still, this claim is highly suspect due to the husband's motives for wanting the arson carried out.