I didn't quite understand the reasoning behind stagnate's actions...

Sinom said:
He "wants their souls" as in he wants them to fight for him. It's like mandatory service for being an undead. You get to live forever in their (according to him) perfect and stagnant world, but you also have to fight for it if your master calls.

Also I didn't watch the anime past Episode 1 and it rushes a few things so I don't know if it's said in the anime, but their deal was that he would take them as soon as their interest in the seal faded, meaning they would no longer be useful there.

I don't remember everything completely because it's been a while since I read it, so I don't remember what you're referring to in your second question maybe someone who read it/watched it more recently can explain that.

Pokenger said:
I have question .
Will Mary and blood remain as undead or will they die(by die I mean will they no longer be)?

KruxKnight said:

lets not get that part spoiled yet, lets wait for the next episode, i get the feeling it might get explained there...maybe

Pokenger said:
No I just want the spoiler so that I will be a bit less sad later.