Alma is a central figure in the narrative of Mecha-Ude, introduced as a mysterious, sentient Mechanical Arm. His existence as a Mecha-Ude is unique, as he is a being from another world that forms symbiotic bonds with human hosts through a process called derization. Alma is discovered in a sealed, cube-like state, having lost all memories of his past prior to being awakened from his long slumber. This amnesia is a core aspect of his character at the beginning of his journey, as he knows neither his own name nor his origin. He is a special type of Mecha-Ude known as the Trigger Arm, which makes him a highly sought-after target for various organizations, including the large conglomerate Kagami Group and the resistance group ARMS.

In terms of personality, Alma is portrayed as serious, brave, and diligent, possessing a strong and somewhat idealistic sense of justice. He is always eager to jump into action and do what he believes is morally right, often displaying a boldness that can border on recklessness, especially when compared to his more cautious partner, Hikaru. Despite his warrior-like demeanor, Alma also has a thoughtful side, showing a deep interest in history and a desire to learn from the past. His personality is often likened to that of a classic cartoon hero, earnest and direct in his actions. Due to his amnesia and unfamiliarity with the modern world, he can also be easily fascinated by mundane objects, finding wonder in things as simple as toilet paper. He enjoys hobbies typical of an enthusiast, such as playing video games, reading manga, and watching anime and movies, though his enthusiasm sometimes leads him to accidentally break game controllers.

Alma’s primary motivation is driven by his innate sense of justice and his desire to protect others. After bonding with the middle school student Hikaru Amatsuga, he becomes fiercely dedicated to his partner, constantly pushing him to do his best and trying to keep him awake and focused. He is extremely confident in Hikaru’s potential. However, this relationship is complicated by a deep-seated trauma from his past. As his memories return, it is revealed that over a century ago, during the Meiji era, Alma had formed a strong bond with a man named Yakumo Kagami, one of the founders of the Kagami Group. A failed experiment to awaken a power called the Ordela led to a catastrophic explosion, and Yakumo died. Consumed by guilt over Yakumo’s death, Alma feared the same fate would befall Hikaru. This trauma led him to briefly separate from Hikaru, believing it was the only way to keep him safe. Ultimately, his motivation evolves from a simple desire to do good to a need to overcome his past guilt and form a new, healthy, and equal partnership with Hikaru, learning to trust in their combined strength without fear.

Alma’s role in the story is that of the titular deuteragonist and the catalyst for the entire plot. His awakening in Hikaru’s presence instantly throws the ordinary boy into a dangerous conflict between the Kagami Group, which seeks to exploit and control Mecha-Ude as weapons, and ARMS, which fights to liberate them. The fact that he is the Trigger Arm makes him the key piece in a larger, more complex game. He is also central to the main conflict of the series, as his brother, a Mecha-Ude named Fist, serves as the primary antagonist. Fist, bonded to a descendant of the Kagami family, holds a deep hatred for humanity stemming from the traumatic events of the Meiji era that also affected Alma. Thus, Alma is not only a participant in the modern-day conflict but is also directly connected to its historical origin, and his final confrontation is a personal one to stop his brother’s supremacist ideology.

Key relationships define much of Alma’s character arc. His relationship with Hikaru is the most central, evolving from a forced and clumsy symbiosis to a deep, trusting partnership. Unlike a standard Mecha-Ude derization, Alma’s first attempt to bond with Hikaru failed, resulting in him attaching himself to the hood of Hikaru’s hoodie rather than directly to his arm. This unique circumstance allows Alma a degree of autonomy unusual for a Mecha-Ude, as he can act and move independently of his host. He often imitates Hikaru’s actions, such as buying the same soda from a vending machine, in an attempt to bond and understand him. Another crucial relationship is with his brother, Fist. Fist is a fellow Mecha-Ude who witnessed the same past tragedy but reacted with anger and a desire for Mecha-Ude supremacy, directly opposing Alma’s belief in coexistence and partnership with humans. The series culminates in a brother-against-brother battle where their conflicting ideologies clash. Alma also has a significant, if tragic, relationship with his first human partner, Yakumo Kagami, whose death is the source of his century-long guilt and inactivity.

Throughout the series, Alma undergoes significant development. He begins as an amnesiac hero, defined only by his desire to act justly. As he regains his memories, he is forced to confront his painful past and the guilt that caused him to seal himself away for over a hundred years. This leads to a crisis of faith in his role as a partner, causing him to push Hikaru away out of a misguided sense of protection. However, he ultimately overcomes this trauma, learning that he can protect his partner without sacrificing their bond. He reconciles with Hikaru and confronts his brother, Fist, not with hatred, but with the understanding that his brother’s hatred is born from a place of love that was twisted by loss. By the end of his story arc, Alma evolves from a guilt-ridden amnesiac into a resolved and reliable partner who has made peace with his history.

Alma possesses several notable abilities that set him apart from other Mecha-Ude. His most distinctive trait is his autonomy; because he is bonded to Hikaru’s clothing rather than his body, he is not limited by his host’s will and can move, speak, and act completely on his own. He demonstrates great physical strength even in his basic arm form, easily dragging Hikaru around and propelling himself through the air with acrobatic skill. He has the ability to shapeshift into different forms, including a two-bell alarm clock configuration, which he often uses to wake Hikaru up. When Hikaru touches the eye of this clock form, Alma can assume his true combat form, covering Hikaru’s right arm and part of his body, which enhances his physical abilities to a great degree. In this state, he can perform a Rocket Punch, launching his hand at an opponent, and a finishing move where Hikaru punches the launched hand from behind to dramatically augment its power and speed. As the Trigger Arm, Alma has the unique ability to generate his own Arbitrium, the energy source that powers Mecha-Ude, and can enter a further fusion state with Hikaru that acts as a Super Mode, drastically enhancing Hikaru’s abilities and changing his appearance.