In the universe of Sengoku Basara, Ieyasu Tokugawa undergoes one of the most dramatic transformations of any character. He is initially presented as a very young and somewhat bratty warlord, a figure who is small in stature but possesses great ambition and a genuine love for his people. In these early depictions, he is far from a capable fighter, and his effectiveness as a leader relies almost entirely on his enormously powerful and loyal retainer, the near-invincible war machine Honda Tadakatsu. So dependent is he on Tadakatsu that he often plays the role of a distressed figure, prone to being kidnapped by other warlords, a nod to his historical experience as a hostage. This leads to him constantly calling for Tadakatsu to come to his rescue, a trait that gives him the image of an over-dependent daimyo.

This image changes completely in the third installment of the series, where Ieyasu is reintroduced as a grown young man of great physique. He has abandoned the helmet and double-bladed spear of his youth, choosing instead to fight with his bare fists, enhanced by powerful gauntlets. This design change marks his evolution from a supporting character into a main protagonist. His personality matures as well, shifting from impatient and whiny to more cheerful, earnest, and trustworthy, though he retains a notable idealistic and sometimes oblivious nature. He is driven by a powerful and all-consuming philosophy: the belief in bonds, or kizuna. His core motivation is to unify the war-torn land of Japan and bring about a lasting peace, not through the tyranny of strength, but through the power of friendship and mutual connection. This makes him an all-loving hero who sees the potential for alliance in everyone, even his enemies, and he is known for extending offers of friendship in the midst of battle.

Ieyasu's central role in the story is defined by a pivotal act of rebellion. After serving under the brutal and power-hungry Toyotomi Hideyoshi, he comes to believe that his lord's methods will never lead to a true or just peace. In a decisive act, he betrays and kills Hideyoshi, an event that shatters his former alliance and becomes the catalyst for a new war. This action creates his most significant relationship, that of a bitter rival with Ishida Mitsunari, Hideyoshi's most fanatical and devoted follower. Mitsunari is consumed by a burning hatred for Ieyasu and seeks revenge for his master's death, leading to the climactic Battle of Sekigahara, where the two face off as commanders of the Eastern and Western armies respectively.

This defining act also creates internal conflict. Ieyasu is a self-aware hypocrite; he wishes to unite the world with peace and friendship, but he knows he must first wage a bloody war to achieve it, destroying many bonds in the name of creating new ones. He is haunted by guilt for what he did to Hideyoshi and Mitsunari, and in a later story, he even lies and claims responsibility for Hideyoshi's death to give the grief-stricken Mitsunari a reason to live on through his hatred, demonstrating a complex and tragic understanding of his rival. Despite his cheerful exterior, he is shadowed by doubt and melancholy, making him a stepford smiler who puts on a brave face for the sake of his cause. He maintains other key relationships as well, notably a deep friendship with the pirate Chosokabe Motochika, which is severely tested, and an unshakable bond with his vassal Honda Tadakatsu, whom he still relies upon even as he fights on his own.

In battle, Ieyasu is a bare-fisted brawler whose fighting style resembles a boxer. His techniques are themed around light, reflecting his heroic intentions. His unique combat mechanic involves charging his attacks, holding down the button to power up his punches for devastating, wide-reaching blows. His signature abilities include Tendōdzuki, a powerful straight thrust punch; Yōganwari, where he slams the ground to create a shockwave; and Koga Genten, where he unleashes a massive blast of energy in the shape of the Tokugawa crest. He can also pull the hood of his jacket over his head, a taunt that increases his attack or reduces his charge time, and his most powerful special attack, Hard Head, is an incredibly potent headbutt. After years of being a leader who could only call for help, he becomes a formidable warrior capable of challenging the mightiest lords in Japan with nothing but his own two fists and the unshakable belief in the bonds he shares with others.