Majin Tantei Nogami Neuro - 01 raw
"Yako’s father was murdered in a locked room. She then meets a man named Neuro Nougami who is a demon from Hell who eats “riddles.” He forces Yako to act as a detective so he can solve mysteries. Neuro longs to eat the ultimate mystery."
1 flat-chested girl, many pretty guys = shoujo.
Comical horror shoujo? I'll pass.