In this volume, we get more backstory from Syaoran. This is not necessarily a bad thing. I'm not much for action sequences, and backstory can be very interesting. In fact, because I have the bad habit of spoiling things for myself via the internet, I know that some of "Tsubasa"'s most memorable story elements are in the backstory. However, you'll have to wait until vol. 26 to get to them.
In this volume, Syaoran tells how he first came to Clow country and met Sakura. He arrives there after his mother has a prophetic dream about someone waiting for him in another world. When they first meet, Sakura is undergoing rights to become a priestess and is not allowed to be touched. Despite this, the two children hit it off. Sakura's mother, though, has been having strange dreams about her daughter's seventh birthday, which is also the final day of her priesthood rights. Syaoran swears that he will protect Sakura at any cost, but what awaits these two when the day arrives?
While a couple of mysteries are unveiled here, they're not especially compelling. And most of the attention is focused on the young Syaoran and Sakura's budding romance. Their relationship is a lot like cotton candy: sugary sweet, but not much substance. But you already know that if you've read the series up to this point.
Overall, this volume is filler. It gives us a lot of fluff instead of really moving the story along. It's not completely terrible; there is some plot, and the art's still really nice. It's one of the weakest volumes in the series, but you kind of have to read it if you want to complete the series. Oh, well, just be glad it isn't Piffle World.