Kara no Kyoukai was written before Tsukihime. Similar world, except no vampires and shit. Just people with above-normal powers.
Also, there are some tiny connections between the two...and in Tsukihime, you can see how characters are similar: Azaka became a prototype for Akiha, Mikiya for T. Shiki in looks, Ryougi Shiki to T. Shiki in powers, Fujino to Kohaku, et cetera.
actually, Fujino's more like Sakura from Fate.
you can sorta see Nasu's works meshing together if you know all three