石畳の緋き悪魔 (Ishidatami no Akaki Akuma)

Background
The story is about a young woman named Layla(ليلى)(played here by MEIKO) who was born to a muslim father and a christian mother living in the. When the breaks out both her parents are killed by the respective opposing sides. When trying to flee, she's shot by soldiers who think she's an enemy and falls into a dungeon. On the verge of death, she finds that there is a demon in the dungeon, who she dubs "Shaytân"(شيطان)(played here by KAITO). He offers her a deal, she'll drink the poison of eternity and transform into one of his kind, in return he will be devoted to her. She agrees and they seal the oath with a kiss, after her transformation, he vows to destroy whichever side of the war she wishes.