Ouritsu Tantei Sion no Ayamachi

The Royal Detective is a private detective employed by the royal family, who seeks out the royal family's interests and covers up any misconduct. Whether it's searching for a lost pet or discussing a breakup with a lover... One of his jobs is to investigate objects known as "Demons of Error," which possess mysterious powers that could be considered curses. Dressed in all purple like a fake magician, the Royal Detective Sion and his assistant, a young girl named Lana, head to a provincial count's house to investigate a portrait crying tears of blood. But what happens next?

(Source: Shueisha, translated)