Mercury waits for her prey, in the shadows. She does nothing to help the victim of an attack, even when a sandy-haired man in a shitennou's uniform extracts a blue crystal from her body and the girl becomes
a monster of the Dark Kingdom, one of its seven great warriors.
Ah, there they are: the sailor senshi, just as she knew they'd come. She's done this
so many times in so many worlds, after all; so many that she's even dreaming of it. Mercury gives a satisfied smirk; but she is not here for them, either. While they battle the youma, Zoisite and Tuxedo Kamen fight over the blue crystal. That is what she's after, and Mercury waits until they're immersed in their battle to dash in under the cover of her own fog and mist to snatch it up. It glows with a strong energy.
Sucess. They notice it, and both chase after her, but she's quickly away, leaving them to conclude it was her alternate. The blue rainbow crystal will never be seen in this world again - and thus, neither will the princess' tool of destruction, the ginzuishou, which requires all seven to come together.
It's while she's making her escape that a pack of youma, sent to reclaim the crystal, corner her and start to press in closer. Even she might have trouble with this many, and her eyes cast about for escape but find none. Fine, then.
"Dark Rhapsody!"
(ooc: help her escape, make her return it, catch her later to talk more about it, anything goes)