Like other CLAMP anime and manga productions, X contains crossover references to other works by the group. Specifically, Subaru, Hokuto and Seishiro come from Tokyo Babylon, while the CLAMP campus originated in CLAMP Campus Detectives.
Steven Blum is the only voice actor out of both the Japanese and English language casts to retain the same role (Seiichiro Aoki) for both this series and the feature film X (1996).
When in Seiichirô Aoki's first scene he comes to talk to his editor and says how "Mr. Maruyama's manuscripts barely made it for publication," he is making an in-joke and reference to Studio Madhouse producer and founder Masao Maruyama, who green-lit both the 'X' television series and movie. In real life, Mr. Maruyama is known to be a perfectionist around the studio, and consequently, he often insists the staff work until the last minute on their projects to be sure they are the best they can be.