Dai San Koujo no Bannou Shitsuji

Synopsis

Rumor has it that if you drop a letter into a certain Suggestion Box hidden somewhere in the Imperial City, a mysterious young man will come and help solve your problem.... This helpful young man is Roth, the butler of the Third Princess, who wields the most powerful magic as her protector. Together with Krell, his mistress, they will solve the case! (Source: Gangan Online, translated)