Keizo Arashi, known widely by his nickname Benkei, is a prominent figure introduced during the final story arc of Tokyo Revengers. He is a tall, muscular man whose physical presence is immediately intimidating. In his late twenties, he has a tanned complexion, a shaved head of white hair, and a trimmed beard, giving him a much more mature and rugged appearance compared to many other characters. His eyes are characteristically wide and unblinking, which adds to his fierce and intense demeanor. He sports piercings in both ears and has large, curved stripe tattoos on his chest and arms. As an executive of the Brahman gang, he wears their uniform, which features ornate lotus designs on the sleeves. In flashbacks to his teenage years, he is seen with darker hair styled in cornrows and a clean-shaven face.

Benkei's personality is defined by seriousness and a lack of patience for frivolous chatter. He is a man of duty who prioritizes his responsibilities to his gang above all else, often acting as a grounding force to remind others of their primary objectives. Despite his high rank within Brahman, his heart remains loyal to the ideals of the first-generation Black Dragon, the legendary gang he helped found. He holds the original principles of this group in the highest regard and reacts with loud, forceful admonishment toward anyone he believes has sullied them, including his own comrades. This hot-blooded seriousness can sometimes serve as a source of comedic relief. In battle, he is extremely fierce and relentless.

Before becoming a founding member of the Black Dragon, Benkei was a powerful gang leader in his own right. He served as the president of Ragnarok, a massive biker gang of over six hundred members that controlled the western part of the Kanto region. His reputation was so fearsome that he was nicknamed Redcliff, said to come from walking through the aftermath of a bloody battle drenched head to toe in the blood of his enemies. Ragnarok was a rival to the eastern gang Kodo Rengo, led by Wakasa Imaushi. Their intense feud only ended when Shinichiro Sano, the future founder of Black Dragon, appeared and unified them. This event inspired deep respect and loyalty in Benkei, who then devoted himself to Shinichiro and became one of his most trusted followers. When the first-generation Black Dragon was formed, Benkei was named the Captain of its Guard Unit. After the gang eventually disbanded, he and Wakasa ran a boxing gym together, where they also served as guardians and mentors to a young Senju Kawaragi, who would later form the Brahman gang.

During the conflict known as the Battle of the Three Deities, Benkei serves as a high-ranking executive of Brahman, one of the three most powerful gangs vying for control of Tokyo. His role is to protect and advise the gang's leader, Senju Kawaragi. He demonstrates his immense authority and disdain for those who have disgraced the Black Dragon name by easily dispatching Shion Madarame, the feeble ninth-generation leader of the gang. When the war begins, he fights alongside his lifelong partner, Wakasa. Together, they are a legendary duo known for their abnormal strength, and they effortlessly take down roughly one hundred members of the enemy Rokuhara Tandai. Benkei also directly confronts South Terano, the leader of Rokuhara Tandai and one of the most powerful fighters in the series. Using his powerful strikes, he initially manages to gain the upper hand, showing his incredible combat prowess. However, South ultimately awakens a deeper, more violent power and brutally defeats Benkei, leaving him unable to continue fighting. After the war, in the final, peaceful future timeline, Benkei achieves his goal of running a martial arts gym, Gojo Gym, together with Wakasa.

Benkei's most significant relationship is with Wakasa Imaushi. What began as a bitter rivalry between gang leaders evolved into a deep, unbreakable friendship and a formidable partnership in battle. They are often referred to as a duo and are considered living legends because of their combined strength. His loyalty to Shinichiro Sano is the cornerstone of his character; it was Shinichiro who ended his war with Wakasa and gave him a greater purpose, earning Benkei's lifelong devotion. He is also a close friend and ally of Takeomi Akashi, another founding member of Black Dragon, and has fought alongside him for many years. Finally, he shares a protective, brotherly bond with Senju Kawaragi, having watched her grow up and supporting her ambition to create Brahman.

In terms of abilities, Benkei is considered a legendary fighter. His greatest asset is his raw physical strength, which he uses to deliver devastatingly powerful punches and kicks, including a notable big boot kick. His large, muscular frame also allows him to withstand heavy blows from opponents without being fazed. His former authority as the leader of the 600-man Ragnarok gang and his legendary status as a first-generation Black Dragon captain give him immense respect and influence throughout the Tokyo delinquent world.