Do you think the relationship of Rikuou and Kazehaya similar to Kurogane and Fai? Kazehaya was born a twin with Kei, running away from his village feel guilty leaving his sister behind similar to Fai running from his country leaving Ashura and his dead twin far away to join the journey. Rikuou was living with his sister Tsukiko before his sister disappeared and he go to the drugstore and meet Kazehaya similar to Kurogane was living with Tomoyo before he banish from his country to the journey and meet Fai.
(Spoilers for both)
Sort of! They definitely have the similarities that you’ve listed, though the way the stories use those similar plot elements is very different in each series. There’s a lot of potential twin comparisons in Clamp, and to me Kazahaya has a lot more in common with Watanuki than Fai, though comparing all of them would be pretty fun. They all have overlapping elements, but in each case the set up of the “twin problem” is very different. (In this case, "My twin is evil" is very different to "My twin is dead and I think I killed them")
I think the same can be said of Kurogane and Rikuo. They both have “the grumpier of the two” and “missing family members” in common, but the actual use of those pieces is very different - Kurogane’s family was super tragically murdered, while Rikuo’s sister is mysteriously missing. And while Rikuo doesn’t know where Kei is, Kurogane knows EXACTLY where Tomoyo is and is trying to get back to her.
I quite enjoy that Clamp aren’t afraid to take a collection of character tropes they’ve used already and re-use them in a completely new context. It can be fun to see all the things that make them different and try to figure out what the story is doing differently each time.