Hmm, I'd say that it's pretty clear that they live in the same world. The settings are too consistent. Magical systems, organizations like the Mage's Association and the Church, almost everything is shared. And while the main characters from each series may not meet each other, I've never seen anything that said they literally cannot -- there just haven't been any circumstances placing them together. Furthermore, secondary characters like DO cross over into multiple series.Message wrote:Actually, the worlds of Tsukihime and F/sn cannot exist together in their natural states. Only through the use of extra-universal bridges (i.e. Ahnenerbe, Carnival Moment, etc...) can people from the different TYPE-MOON sub-universes meet each other. But this is an different topic altogether, and the discussion becomes so meta that it cannot make any sense even if you'd believe in the TYPE-MOON universe.. So let's stop it here. >_>
Places like Ahnenerbe are used as an excuse to bring the whole cast together for no real reason -- they're basically non-canon stages used for gag material.