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)

A boy, Serel, who works as a librarian at a certain royal magic library. He claims to be "just a librarian," but he chats with his childhood friend, Princess Fiona, manipulates advanced magic, and handles a huge workload all by himself; no matter how you look at it, he is not "just a librarian." Source: MU

Roth is a genius magician who wields the world's strongest defensive magic. His job is to guard Krell, the world's cutest and most adorable little princess. One day, Roth receives a request to protect the “magic key,” a national treasure. The two set out on the job, but it soon develops into a major incident that shakes their and their country's fates... "My butler will come save me, won't he?" The master-servant tale between an ultra-kawaii princess and her sharp-tongued butler is about to begin! (Source: HJ Bunko, translated)

To protect the Angel, the strongest Grim Reaper steps in— The Brugel Kingdom, known as the land of knowledge, boasts numerous libraries. Within the royal capital lies the Forbidden Library, which houses only cursed books and texts containing abilities that could destroy the nation if misused. Kumura, the Chief Librarian possessing omniscient power, and Vil, the Assistant Librarian wielding the power to bring death to all things, manage, seal, and protect these forbidden texts. As Kumura and Vil oversee the library, the seal on a forbidden book is suddenly broken, and a giant shrouded in mist appears. To reseal it, Vil confronts the giant, using the power known as the Grim Reaper!! Just after resealing the book, Vil receives an offer from a hostile empire seeking the Grim Reaper's power. Vil is attacked in retaliation for refusing the offer, and Kumura is put in danger—! Enraged, Vil unleashes their true power!