I'm really confused as to whether Shiki Nanaya is the master or servant of White Len. At first, he seems to act as a Familiar created by White Len, but then he says that he'll be a good master to White Len. There's also the fact that he only came into physical existence outside TATARI because of White Len, since every other appearance outside Melty Blood he has been a persona of Shiki.
So, is he White Len's master—like how Shiki is Len's Master—or are the roles reversed, and she is the master keeping his physical existence in the world (as Familiars can only be in the world if supplied with prana from their master)?