The Strength to Fight is the 4th chapter in Tsubasa: Reservoir Chronicle.
Sorata explains that Hanshin is known as the "country of the tiger," and continues to explain to the trio some facts about his country. As he's explaining, Kurogane falls asleep, but awakens when something hits him from above. Sorata explains that he did this with the aid of "kudan" and that everyone in Hanshin is haunted by one. Arashi, who was a former sorceress, goes on to say that even though the three of them come from other worlds, they too, will be haunted by a kudan. She also warns them that if there are other people who desire to obtain Sakura's memories, conflict will arrive and that they will need need the power to fight should this happen. Their kudan will help them.
Mokona confirms that one of Sakura's feathers is located in Hanshin, though it is currently far away. Fai & Kurogane confirm that they will help Syaoran in his quest. Sorata and Arashi offer their guest room until they leave the world. While Fye and Kurogane move to a different room, Syaoran chooses to stay with Sakura. He refuses to leave her, but Arashi advises him to rest, as one can never tell when he'll be able to sleep again. In his dreams, Syaoran sees a vision of one of the kudan, who offers him power based on his heart's strength and his wish to protect his most precious person. Syaoran wakes up with a start, feeling heat in his chest.