Tsubasa Reservoir Chronicles is my most favorite anime so far. The plot is very confusing at the start, I was at lost when I learned that there were two Syaorans and two Sakuras at the same time. I actually thought and hoped that the other Syaoran-Sakura pair were from Cardcaptor Sakura, but they were not. But later on, as I finished the series (following the manga storyline and the OVA), everything became clear to me. I was overwhelmed at how deep, detailed, and complicated the plot is; I cannot comprehend it in just one sitting.
So the Sakura who lost her memories/feathers, and the Syaoran who traveled to search for them are the cloned ones, meaning they were only created for the sole purpose of gathering power for Fei Wong Reed’s ambition: to travel through dimensions without compensation. The cloned Sakura was created from the real Sakura as body and soul, while the cloned Syaoran was only created as a body and only meant to follow directions – which was to gather feathers no matter what it takes (even he would have to kill somebody). But the real Syaoran managed to put half of his heart to the clone so he wouldn’t act mercilessly, and real Syaoran thought that the clone would later grow his own heat in his journey. That action lessened real Syaoran’s power and so he waited until he was able to overcome Fei Wong’s imprisonment.
I will end my storytelling at this point. It’s advisable to read the manga since the plot is all there, though the anime would only follow the manga storyline until episode 41 (I think). The OVA are also must-seen. The nice advantage in this anime is that it’s very possible to do crossover into other anime; who knows what kind of world would the gang end in search for the feathers, and also when Syaoran, Fai, Kurogane and Mokona travel endlessly for the sake of traveling (in the case of Kobato).
XXXholic is very much connected in Tsubasa Chronicles since it’s Yuuko who granted their wish to travel, and she was also somewhat acquainted to Clow Reed (maybe they even shared an intimate relationship). Watanuki Kimihiro is also Syaoran’s another existence; filling his gap in another timeline. I could also say that Cardcaptor Sakura also shared some connection with this anime. Clow Reed was partly responsible for the happenings in Tsubasa Chronicles since he’s related to Fei Wong Reed. In addition to that, Kinomoto Sakura briefly appeared in Tsubasa Shunraiki OVA as a guide to clone Sakura when she was on the verge of death. Kinomoto Sakura also donated her star staff to Yuuko as payment to real Syaoran’s travel to Clow Country.
I think it would be funny and interesting to see Syaoran and Sakura of Tsubasa Chronicles meet with Kinomoto Sakura and Lee Syaoran of Cardcaptor Sakura, as well as Watanuki Kimihiro of XXXholic. Just my thought! And lastly, Syaoran and Sakura share the same name, Tsubasa.