This is the Hifuu Detective Agency

Maribel Hearn and Renko Usami are two mostly-normal college students with a penchant for uncovering supernatural secrets. When one of their investigations leaves them trapped in Gensokyo 80 years in the past, they find themselves wrapped up in a string of dangerous Incidents that compel them to do what they do best: Reveal the secrets of this world as the Hifuu Detective Agency! Covers incidents from a lot of Touhou Project videogames.