Mark Twain is typically a jovial and cheerful individual, standing out among his fellow Guild members with his laid-back demeanor. He often suggests leisure excursions for the group, though his ideas are usually rejected. Despite this, Twain maintains a close bond with his colleagues, expressing fondness for the Guild even after its dissolution, describing it as a “rather nice place.”

As one of the Guild’s snipers, Twain takes great pride in his marksmanship and his ability. He meticulously records his achievements involving his sniping skills in a personal “success diary,” showcasing his dedication. Twain also frequently praises his doll-like companions, Huck and Tom, for their exceptional marksmanship, doting on them as if they were real partners.

However, beneath his lighthearted and confident demeanor lies a serious side, especially evident during combat. Twain approaches battles with a focus on challenging his sniping skills, notably against opponents like Atsushi Nakajima, whom he considers his strongest adversary and notes in his success diary. Despite his confidence, Twain is not above acknowledging an opponent’s prowess, graciously and amicably accepting defeat when bested by a skilled adversary. This mix of pride, camaraderie, and humility defines Twain’s character, making him a unique figure within the Guild.

Mark Twain has dark orange hair styled outwardly, complementing his striking green eyes. His attire is casual yet distinctive, featuring a long white shirt with buttons that are perpetually undone, paired with black pants and suspenders that hang loosely. Twain opts for black sandals as footwear, adding to his relaxed look. Accessories include black bracelets around his ankles and two brown bands adorning his left wrist, further accentuating his laid-back and unconventional style.

Mark Twain’s background remains largely unknown, with no detailed accounts of his life prior to his involvement with the Guild or his motivations for joining. However, it is suggested that Twain has been dedicated to his “success diary” for a significant period, potentially beginning the practice during his time in his hometown. This diary reflects his pride in his marksmanship and serves as a record of his achievements, hinting at his long-standing commitment to honing his skills.

Mark Twain’s ability, Huck Finn and Tom Sawyer (ハック・フィン&トム・ソーヤ, Hakku Fin & Tomu Sōya), manifests as two doll-like entities named Huck Finn and Tom Sawyer. Through this ability, Twain can achieve unparalleled accuracy in shooting by attaching either Huck or Tom to his bullets. This ensures that his shots reach their target with absolute precision.

Additionally, since Huck and Tom are mentally linked to Twain, they can also be used for long-distance surveillance. This feature allows Twain to gather information or monitor situations from afar, making his ability both a formidable offensive tool and a valuable resource for reconnaissance.

Mark Twain first appears alongside Howard Phillips Lovecraft, John Steinbeck, Nathaniel Hawthorne, Margaret Mitchell, and Herman Melville during the intense confrontation between Kōyō Ozaki, Atsushi Nakajima, and Kyōka Izumi. As the three-way war escalates, Twain takes on the role of a sniper, targeting Atsushi and Kyōka to assist Francis Scott Key Fitzgerald and Herman in capturing Atsushi.

Later, after Atsushi escapes from the Moby Dick, Twain attempts to prevent him from safely landing in Yokohama by deploying his sniper skills and ability. Although he successfully punctures Atsushi’s parachute, forcing him into freefall, Atsushi transforms fully into a tiger, allowing him to land unharmed. Twain continues to relentlessly fire .50-caliber bullets at Atsushi, but the latter manages to evade them. Surprised by Atsushi’s agility and endurance, Twain shifts his strategy, shooting a tanker truck in Atsushi’s path. The resulting explosion severely injures Atsushi, and Twain follows up with a barrage of shots, ultimately immobilizing him.

Declaring Atsushi as his greatest adversary and noting this encounter in his “success diary,” Twain prepares to end the battle. However, Osamu Dazai intervenes, nullifying Q’s curse by touching the doll and deploying a saturation chaff smokescreen, jamming Twain’s sensors and radar. Acknowledging the strength of Atsushi’s bond with his allies, Twain admits defeat with a jovial demeanor.

After evacuating the Moby Dick, Twain accompanies a captured Lucy Maud Montgomery, bickering with her as they disembark from a helicopter. Turning to Louisa May Alcott for guidance, Twain humorously suggests they all go to karaoke, but Lucy stomps on his foot in frustration. Ultimately, Twain leaves the area with Steinbeck, Louisa, and Lucy to avoid the Moby Dick’s collapse.

In the aftermath of Fitzgerald’s defeat, Twain discusses the Guild’s uncertain future with the other members. Reflecting on how great the Guild once was, Twain asks Steinbeck and Louisa about their plans. When Steinbeck decides to address the internal strife among the Guild’s remnants, Twain is shocked, recalling Steinbeck’s previous disdain for Fitzgerald. Ultimately, Twain chooses to return home to complete his autobiography. Before parting ways, the group encounters Lovecraft, who mentions the completion of his “contract” before jumping into the ocean to sleep. Twain expresses curiosity about Lovecraft’s true nature, prompting Steinbeck to remark that Lovecraft was one of his few friends.

The name Mark is of Old Latin origin, meaning “consecrated to Mars,” referring to the Roman god of war.

The surname Twain is of Old English origin, meaning “divided in two” or “twofold.”