On the first day of their new school term, a model airplane accidentally makes a dive towards Yuna, but it is quickly stopped by a thrown kunai.

At the bowling alley, Yūna wanders into the men's restroom and interrupts a yakuza deal involving fake dolls.

The story continues as new characters enter Yūna and Mamoru's lives with both good and evil intentions, wacky adventures, hints of romance, and confrontations with the strangest of adversaries.

The light novels were adapted into a 12 episodes anime series by the Group TAC studio and produced by Aniplex.

Between July 16, 2008 and January 21, 2009, DrMaster published the English translation of the first three volumes of this series under the name of Mamoru the Shadow Protector.