Lunar Month

Yuuko Ichihara, a main character in xxxHolic, repeatedly talks about Clow. While the exact nature of their relationship is uncertain, they are known to have worked together to create the two Mokonas who appear in xxxHolic and Tsubasa. Fei Wong Reed, who appears in Tsubasa: RESERVoir CHRoNiCLE, is also Clow Reed's relative, and considers Yuko and Clow as barriers.

Clow Reed is mentioned in Tsubasa: RESERVoir CHRoNiCLE, and he was personally acquainted to Yuuko Ichihara. The two together created the Mokonas that would help Syaoran, Sakura, Fai and Kurogane travel across dimensions. Fei Wong Reed, the mastermind who initially guides the journey of Sakura and Syaoran across the dimensions, is an ancestor of Clow Reed's; though Fei Wong refers to Clow as an interloper in his affairs. The original "Syaoran" is also a blood relative of Clow Reed (through his parents, Sakura and Syaoran Li).

The Clow Kingdom's own variation of Clow Reed was the father of Sakura and Touya, and the former king of the Kingdom of Clow. Little is known about this Clow Reed as he died before the story began. He was known to have allowed the excavation of the ruins in the country under the direction of the archaeologist, Fujitaka, and also allowed Fujitaka's adopted son, Syaoran, to become a close friend of his daughter Sakura (in the altered timeline). It is implied that he had powerful magic of his own and was able to discern the fates of Sakura and Syaoran before his death; he would later teach Yukito, the current High Priest of Clow, his knowledge of magic. It is also implied Clow was unaffected by the changes to the timeline made by both Syaoran's wish to get back the Sakura he met and Fei Wong Reed's plan.

Tsubasa Reservoir Chronicle 190 reveals that Fujitaka, and not Clow, was the King of Clow Country and Sakura's father in the original time line.