Tensai Kyuuteigaka no Yuutsu - Do S na Juusha ni "Dansou" ga Barete Odosareteimasu

Gerald Rügner is a boy artist with a reputation as a genius. In fact, Gerald is actually a girl named Giselle disguised as a man! When she goes to the castle to see a painting by a famous artist, her true identity is discovered by Logan, the mean-spirited squire of the Prime Minister!
Giselle is threatened to do what he says in exchange for his silence, and her prodigious painting skills are used to help him find the murderer of a suspicious death in the royal palace and for some reason, everyone around her recognizes her as his lover, and Logan teases her and touches her...!

"This guy is too much of a douche!"