[the.Merines]

You're right Lost. Suigintou apparently was purported to have killed one of her previous Mediums. Now, here I will attempt to justify why the manga and the character drama can exist in the same universe.

The character drama takes place during season 2. It's a fact that Suigintou forgot certain elements of her life after she was defeated by Shinku. Her memories were only regained after something triggered her to remember. Thus, it makes sense that she would not remember her previous Medium/s, especially if it had been several decades.

On the same note, the status of Suigintou's "sleep" is relatively unknown in seasons 1 and 2. The manga shows that Megu was her Medium from the beginning of the story. However it also shows that Gin kept her box in an abandoned church until it was torn down. In the anime it is never made clear if she sleeps or not, but Gin herself tells Souseiseki that the dolls suffer when they aren't allowed to sleep in their box. This could also be a part of Suigintou's memory problems.