What is the Name of this action comedy manhwa mc had dark brown hair?, (he had a monocle ?...

What is the Name of this action comedy manhwa mc had dark brown hair?, (he had a monocle ?) and a hat. he was on a train and someone dies instead of him ? He takes his place as a teacher and teaches magic and he is in a organisation and try to take information from them and a blue haired ?detective girl is searching, looking, for him