this story is linked to xxxholic. they go one and one. chaorin has something to do with the main character

Nah I wouldn't say it was incest. They were reborn again (reincarnated, maybe that bit wasn't clear), so RSyaoran's mum sakura would have a different genetics to the original sakura. The souls were cloned but it still is confusing to understand some parts. Maybe because they were reborn again and because of their nature and existence was cloned, they looked exactly like the originals. What I am trying to say is that say somebody is reincarnated, it doesn't necessarily mean you will be born in the same bloodline. Plus CSyaoran had powers which he inherited from the Li Family which he didn't before his rebirth. Gah, I get more confused as I think about this...

I think it was a decent, if not above-average ending. CLAMP did a sufficiently good job in explaining why and how it ended: if you don't understand their reasoning, go re-read; if you don't agree with their reasoning, just remember that the world is fictitious.

The only other way it could have gone was for the main characters to endlessly sift through the millions of worlds untouched so far. That would have been boring, repetitive, and the really stupid thing to do. I think the pacing was - as far as the word can take me without Mayuri Kurotsuchi drugging me - perfect.