Arachne

Arachne is actually Kurai's older brother and was told that he was heir to the throne. When Gehenna was attacked and destroyed, he discovers that he was only a decoy to protect the true heir, Kurai. He initially despises her and sells his soul to Lucifer through the Mad Hatter... who seals a spider demon in his chest. He then poses as her cousin to get close to her and kill her, but grows to genuinely care for her. He is responsible for Voice's death when Voice finds out who Arachne really is. He sacrifices himself to be the 999th bride of The Demon Lord to save Kurai.