She's the only female member of the Dark Five. Unlike Pisard and Gekidorago, who make a whole production out of summoning Zakenna, she's way more subtle about it—just a snap of her fingers and she's good to go. Her go-to move is taking human form to get close to the girls and earn their trust before she strikes.
In her true form, she's basically a vampire. Pale skin, all-black outfit with red accents, a cape, fangs, and those distinctive yellow and red eyes rimmed in dark makeup. Her long red hair completes the look. Her brother gives her grief about it pretty regularly, which she's clearly used to dealing with.
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