In Melty Blood, is Shiki Nanaya the master or servant of White Len?
White Len's contract with Nanaya (this is the supressed personality of Tohno Shiki, from Tsukihime) is a symbiotic (yet seemingly contradictory) one -- she maintains his existence with her TATARI powers, while he supplies her with the prana she needs to survive.

However, in the White Len ending in Act Cadenza, Nanaya clears states that he is in the "master" role:

http://www.youtube.com/watch?v=i4O_rLYRESs#t=454s