Arugo, whose full name is Argo Tsukishima, is a character in Guilty Crown who serves as a member of the resistance group known as the Undertakers, also referred to as Funeral Parlor. He is a capable and seasoned operative, often working alongside his comrade Oogumo. Arugo is a young man of average height with a lean, athletic build. He has sharp features, dark eyes, and short, messy black hair. His typical attire reflects his practical, no-nonsense role as a soldier, usually consisting of dark, functional clothing suitable for combat and covert operations.

In terms of personality, Arugo is characterized by his directness, strong sense of justice, and loyalty to his cause. He is not one to shy away from confrontation, especially when he perceives an injustice. This is most prominently displayed when he directly challenges the tyrannical system implemented by Shu Ouma at Tennouzu High School. Arugo serves as a critical outsider’s perspective, highlighting how Shu’s leadership has become corrupted by fear and a rigid class system based on Void rankings. He openly insults Shu for merely pretending to be the group's former leader, Gai Tsutsugami, and for abandoning the very principles the resistance was built upon. Despite his aggressive methods, his motivations stem from a genuine desire to help others and to uphold a moral code, as seen when he attempts to rescue Arisa Kuhoin and the trapped students.

Arugo’s primary role in the story is to act as a foil to Shu Ouma during the arc where Shu seizes control of the school. While Shu descends into a dictatorial mindset, implementing a system where students are classified by the usefulness of their Voids, Arugo remains a staunch opponent of this oppression. He arrives in Tokyo specifically on a mission from Arisa Kuhoin’s grandfather to rescue her, placing him in direct opposition to Shu, who refuses to release Arisa due to the strategic value of her Void ability. This confrontation culminates in a physical fight where Arugo, a trained fighter, manages to gain the upper hand on Shu, showing his superior combat skills even against the Power of the King. His presence serves to show the difference between a natural, seasoned fighter and a young man who relies primarily on his borrowed power.

Key relationships for Arugo include his partnership with Oogumo, with whom he frequently carries out missions, and his connection to Arisa Kuhoin, whose rescue is his primary objective during a significant portion of the narrative. He also shares a professional, if not critical, relationship with Shu Ouma, whom he sees as an inadequate and ultimately failed successor to Gai. His notable ability is his Void, which is manifested as a torch. When extracted and used by Shu Ouma, this torch emits a powerful black substance with properties similar to a black hole. This darkness effectively traps anything caught within it, preventing escape. Its nature is described as the light that brings darkness, directly contrasting typical light-based abilities.