Question: are all fate series related?
Answer: Nasu and Takeuchi's novel series Kara no Kyokai also got a commercial released by Kodansha in 2004 and later got a series of anime movie adaptations by anime studio ufotable from 2007 to 2013. Tsukihime, Kara no Kyokai, and the Fate series are all set in parallel versions of the same world.