Kojuro Katakura is introduced as the trusted chief retainer and primary strategist serving Date Masamune, the leader of the Date clan. He is widely recognized as the right-hand man of the One-Eyed Dragon and is often referred to by the epithet the Right Eye of the Dragon, a title reflecting his role as the tactical and moral compass for his lord. His physical appearance, featuring a prominent scar on his cheek, a shaved or tightly slicked-back head, and his direct, stern manner of speaking, is deliberately modeled after a traditional yakuza gangster archetype, giving him an imposing and authoritative presence.

Personality and motivations are deeply rooted in an absolute code of honor and unwavering loyalty. Kojuro is calm, collected, and disciplined, serving as a grounding force for the energetic and often reckless Masamune. He values honor above all else and once demonstrated this by willingly facing execution for the transgression of drawing his sword against his own master, even though his actions were taken for a just cause. His primary motivation is his profound and steadfast faith in Masamune's potential. He firmly believes that the young Date lord is destined to become the future ruler of Japan, and he dedicates his entire being to fulfilling that ambition, guiding him with both wisdom and discipline.

In the overarching narrative, Kojuro functions as more than just a vassal. He acts as a mentor, a brotherly figure, and the emotional anchor of the Date faction. He is the only person capable of calming Masamune when the young lord loses sight of his surroundings. His role becomes particularly crucial during periods of Masamune's weakness. When Masamune loses his right eye and falls into a state of despair, causing his other retainers to abandon him, Kojuro remains fiercely loyal. He stands by his lord, delivers a harsh reprimand to those who mock the fallen leader, and ultimately restores Masamune's will to fight, reaffirming his faith in him. This act solidifies his role as the one who bestows hope and the identity of a leader upon the One-Eyed Dragon.

Key relationships center almost entirely on Date Masamune. The bond between them transcends the typical master-servant hierarchy, resembling a deep brotherhood built on mutual trust and respect. Kojuro taught Masamune swordsmanship and political strategy, and though he occasionally turns a blind eye to Masamune's wilder antics, he is fiercely protective. Other characters frequently acknowledge Kojuro's own immense skill; figures such as the master strategist Hanbei Takenaka have noted that Kojuro possesses the talent and intelligence to rule a country on his own, but he chooses to serve Masamune out of pure loyalty.

The character undergoes notable development by exploring the depth of his commitment. While initially the perfect and unwavering shadow, his role evolves as his influence over Masamune's path becomes explicit. He is not merely a follower but a shaper of the future, guiding his lord from reckless youth into a purposeful leader.

In terms of notable abilities, Kojuro is a supremely skilled and intelligent warrior. He is the only left-handed swordsman in the cast, giving him an unusual stance and attack pattern that his enemies struggle to read. His swordsmanship is so refined that it is frequently hinted by other characters that he is actually stronger than his master, though his humility and loyalty keep this potential in service of Masamune rather than personal ambition. Beyond combat, his greatest weapon is his strategic mind, which has led the Date army through countless hardships and victories. A surprisingly peaceful hobby provides a contrast to his warrior reputation: he has a deep passion for gardening and growing vegetables, a quiet pastime that reflects a more serene and grounded aspect of his complex personality.