Kurokishiro Nite Hebi wa Naku

When the memories of a distant day heal your cold heart, the truth you see is one. Once upon a time there was a kingdom called Gilnavia. In a large castle built in that country, the king Zairud and his queen Rushana lived with their many servants. One day, Zairud made a ``certain contract'' with Azerazar, the god of this world. That contract comes at a price, in exchange for keeping the promise to God. He promised wealth and life. However, there is one memory that Zairud cannot remember...? A sad and solemn black fanta about a brutal king and a benevolent queen. https://www.cmoa.jp/title/224814/