The Whereabouts of the Feather is the 10th chapter in Tsubasa: Reservoir Chronicle.
Once the smoke of Primera's blast cleared, Kurogane grunted that Fai was okay. With his kudan's help, Fai evaded Primera's attack. Undaunted, the girl continued her barrage of sonic attacks -- Fai smoothly dodging them all. Syaoran, seeing how close the fight has become, still wanted to go up to help. However, Kurogane assured him that Fai knows what he's doing. From his own experience with a kudan, Kurogane said that while the kudan endows the power of flight, Fai's fighting skills are his own. In the short span of the time they've been on this journey, Fai has honed his battle abilities and gotten used to fighting.
Wishing to quickly end the fight, Primera transforms her kudan into a different form. In this new form, the kudan is able to put people under her trance. The blasts swiped Fai, but he was again unhurt. He mused that Primera's kudan probably isn't the one containing Sakura's feather -- as strong as Primera and her kudan, Mokona has not reacted one bit.
Primera attacks again, and this time, Fai swoops swiftly up to her directly and pins her down: "I don't want to have to hurt such a cute girl...Why don't you just give up?" Primera shrieks, not realizing that her kudan was still on. Blasts emate from the microphone and hits the castle roof, where Masayoshi and Mokona were still dangling.
Masayoshi was falling. Mokona was falling. Masayoshi's kudan came out to save him.
In the midst of the crowd below, Asagi showed up and asked Primera what's happening. At the same moment, Mokona perks up: a feather was close by!