Tantei Xeno to Nanatsu no Satsujin Misshitsu

The story follows Detective Xeno, who after being found collapsed at the side of a road covered in blood and was taken to a hospital the first thing he said upon awakening was solving a murder that happened in the hospital! Xeno himself has no memory of who he is or where he came from, but after that huge incident and after leaving the hospital, he opened up a detective agency and in just a year he solved some high-profile cases.