Hakoniwa no Fräulein

While looking for a ghost that helped him as a child, Satou Akira has run into a fair amount of spirits that he doesn't even see. One day, he goes to a supernatural detective agency for help, and he meets the adorable Yui and her devoted butler Kujou. Using her power, Yui ends up helping him with a number of the dangerous supernatural troubles he gets himself into. Akira starts to feel attached to the detective agency, and wants to learn more about the supernatural!

(Source: MangaHelpers)