Raimeiki

Raimeiki is a high-ranked, possession-type demon of the Black Demon Series. She formed a contract with Kureto Hīragi and became his Cursed Gear.

Raimeiki manifests as lightning surrounding the blade. In chapter 58, her true form is revealed to be of a young woman with sharp slanted eyes, a black horn protruding from her forehead, and long unkempt hair that is held down by a black wide headband that sits behind her horn with some strands sticking out. As a former vampire, she has pointed ears and fangs, which adds to her wild looking appearance.

Her outfit is the most revealing of the demons so far as her black, extremely revealing dress consists of cloth strips, with two wide enough to cover the front of her breasts while the rest are thinner and tied around her upper arms near the shoulders down to her stomach that goes down to a short mini skirt. She wears a long black scarf, and matching, long, arm length fingerless gloves, while her legs are covered past her knees in what looks like shadow.

(Source: Owari no Seraph Wiki)