-On the whole Kurumi thing-
Kurumi 'gaurded' the lake of blood for unknown reasons, perhaps after LLS she got fed up and did something else with her time, however, for this to be true Kurumi must have taken up the position as gaurd of the of her own will.
I believe she's also good friends with Elly (I've read it somewhere), so perhaps she resides at the lake to keep in close touch with her friend, I dunno I makin shit up again.