It's a bit late, but let me try.
As for the "how", it is possible for a Rozen Maiden to just give up her Rosa Mystica. IIRC, there are several instances where a doll just asks another to give it up, and later in the Tales Suiseiseki lends her own Rosa Mystica to Souseiseki.
But maybe it also has to do something with Souseiseki atacking her master in a way (his delusions at least).
Even in the anime, Suigintou's "exploding heart punch" thingy wasn't that hard a blow; it seems to be rather symbolical, the bodies don't have to be damaged beyond repair.
As for the "why", this seems to be more tricky. She might have tried to make sure her master (the current or any future) can't ask her to do something like this again by depriving him of his "tool" (herself).
Maybe it was just a sense of loyalty, after a lost fight (fight not in the literally sense, more like a lost cause) taking the own life, read: committing sudoku. The Japanese way of dealing with such situations. Or some kind of atonement for her sins, fighting her own sister, perverting her abilities as a gardener, using them to kill instead of protecting.
Last edited 13/01/01(Tue)14:27.