The Kudan of Flame is the 11th chapter in Tsubasa: Reservoir Chronicle.
Shougo arrived to see the ruckus created by Primera and Fai's battle. He's annoyed that instead of getting ready for her concert, she's out here battling... and destroying important city monuments. She whined that battling with her kudan would be the only way to get him to notice and play with her. He retorted that he does have other things to do with his time: he has to go to school and help out with his family's business (as a matter of fact, he was in the middle of a delivery!).
Meanwhile, Mokona was getting excited as it told Syaoran how it again felt the surge of power from Sakura's feather, but like last time, it went away as soon as it came. Syaoran remembered what Sorata told him about the nature of the kudan: how it becomes more powerful when it's protecting its owner. They decided that the only way to get Sakura's feather back is through battle. Shougo, seeing Syaoran's intent, challenged him to battle. They both unleashed their special-class kudan, but despite seeing the full power of Shougo's monster, Mokona still did not detect Sakura's feather. Their fight begun, each side impressively utilizing the full power of their kudan. Shougo was impressed by Syaoran's skill, commenting that the kudan's strength is proportional to one's strength of heart -- what is it that's making Syaoran so strong? Syaoran simply replied: "There is something that I have to do." Shougo nods in understanding. With a warning yell to his comrades, he unleashes his most powerful move: letting loose a raging flood to cover Syaoran and the rest of the battlefield. Masayoshi cries out in alarm, but thankfully, Syaoran and his kudan were able to defend themselves from the fatal attack. Through his tears, Masayoshi couldn't help but be in awe of Syaoran. He had been only in Hanshin for a few days, and already he had total control over his kudan. Masayoshi promised himself that he, too, would become stronger, just like Syaoran.
Above them, the castle was starting to collapse. Masayoshi shields Primera from the falling debris, vowing that he was no longer going to run away. He releases his kudan, which was once so small, but which now loomed large over the castle. Mokona's eyes perk up: that kudan is the one carrying Sakura's feather!