The Proof of Bravery is the 12th chapter of Tsubasa: Reservoir Chronicles.
Despite their surprise that Masayoshi's weak kudan was the one that they were searching for all along, Fai realizes the reason why Mokona couldn't detect the presence of the feather. The power of Sakura's feather only appears when this kudan is protecting its master in a life-or-death situation. Mokona first felt the surge (mekyo!) during the street fight, and then again when the kudan became super-sized to protect Masayoshi from the crumbling castle.
However, the sudden rush of power makes the kudan uncontrollable. It sends out an explosive blast, throwing Primera off the roof. Shougo rushes in with his own kudan to rescue her, and they could only watch in horror as the kudan continued to destroy the rest of the building with its fire attack. Despite Masayoshi's pleas and reassurance, the kudan riled on. Now that he knows where Sakura's feather is located, Syaoran sets out to retrieve her memory from the kudan. Kurogane warns him that it's reckless to fight something so big and so out of control. One mistake and it's over. Syaoran reassures him that he wouldn't die; not when he still has something to finish. Fai tells him to go, that he and Kurogane (actually, mostly Kurogane) will handle things in the meantime.
They watch him fearlessly fly off to his task, his kudan of flame at his side. Fai comments that Syaoran is strong in a lot of ways, and that he finally understands why that kudan chose to be at Syaoran's side.
Syaoran reaches Masayoshi, who himself is in tears, yelling at his kudan to stop. Syaoran tells the other boy that he found what he was looking for, and it happens to be inside Masayoshi's kudan. Masayoshi also has noticed the sparkling feather located deep within the kudan's chest. Syaoran dives in to retrieve the feather, ignoring Masayoshi's words of warning. The gigantic kudan is going berserk, and Masayoshi is afraid that his kudan's power will kill Syaoran.
With the feather just a few more inches beyond his reach, Syaoran pushes forward. In doing so, not only is he hurting the kudan, but Masayoshi as well. It appears that whatever pain the kudan is going through, Masayoshi feels as well. Nonetheless, he tells Syaoran that if the item Syaoran is looking for is in the kudan, and he should have it -- despite of the pain he and his kudan are experiencing right now.
Syaoran reaches out and clutches on to the feather. With the power gone, Masayoshi's kudan returns to its normal size. As the battle ends, they all feel drops of water splashing on them, courtesy of Shougo and his kudan. Syaoran barely notices, as he gazes in awe at his reward. In his hand, he finally has one of Sakura's feathers of memory!
- The second of Sakura's feathers retrieved.