Tsubasa: RESERVoir CHRoNiCLE Volume 04: 08/12/12
Volume 4 of Tsubasa: Reservoir Chronicle by CLAMP is where the consequences of Sakura's missing memories and Syaouran's bargain with Yûko begin to take shape.
Sakura has her first memory restored where Syaouran was present. She remembers her conversation but not him. It's like the Garfield Minus Garfield strip. Call it Syaouran minus Syaouran. Sakura notices the glitch in her memory and that causes even more discomfort.
This volume also introduces the idea that the feathers are powerful and valuable things. They are also things that have gone across all time and space.
They arrive in a world with a legend of a princess who kidnapped children after the death of her parents. Now the children are being kidnapped again and the villagers suspect her ghost. At the heart of the legend is one of Sakura's feathers which as been waiting for her for decades.
Pay attention to Sakura's ability to see the ghost princess. This ability will become more important as the series progresses. It will also help draw connections between Sakura and a similar character in xxxHolic.