Some TMNT stuff really isn't for little kids.
Leonardo's daimyō is an unnamed but important character appearing in Tales of Leonardo: Blind Sight. Leonardo experiences a vision of another life where he is a samurai in feudal Japan, having been born to the turtle demon Kappa and raised by Kubira the rat of the Japanese zodiac, but has become a vassal of this particular daimyō.
Leonardo's daimyō betrays his vassal by stealing a pair of katana Kubira had given them, framing the turtle for their theft, and banishing him from the village, threatening to kill the turtle's wife and daughter Yumi if he should ever return. The daimyō then sends the masked Yumi to assassinate him, but when confronted with the turtle, Yumi disobeys her orders and refuses to kill her father. Leo instructs Yumi to sneak back into the village and spirit her mother to safety.
Leo confronts his former daimyō, discovering him with his "stolen" swords. The daimyō had heard rumors of his former vassal's origins, and that Kubira had given the adopted turtle a pair of magical swords that focus the bearer's fury, and draw in and cut objects in their path. Kubira had sent the turtle to kill Kappa, but the turtle disobeyed his orders and refused to kill his father. The daimyō coveted these swords for himself, hoping to become undefeatable in battle. He admits to hoping the turtle would have killed his own daughter, discovered her identity, and then killed himself in shame, but she ended up disobeying orders and refusing to kill her father, just as the turtle had once done.
The daimyō attacks the unarmed turtle with the swords, missing the turtle at every swing, but soon succumbing to fury and losing control of the swords. Leo manages to disarm the daimyō, and both katana fall at the feet of the statue of Kubira in the daimyō's audience chamber. The statue tips over, knocks over a torch stand, and a fast-spreading fire engulfs the daimyō's castle as Leo makes his escape.