One fateful day, Inaho -- a model catholic high school student -- meets a vampire named Mosquiton and his two sidekicks: Honou and Yuuki. Joined by a gorgeous wolflady and a kindhearted brute, they set out to search for the mystical items called "O-parts". These mysterious treasures, difficult to obtain, are rumored to give incomprehensible power to the one who manages to obtain and activate them with an O-part key.
Ever been mistaken for a member of the opposite sex? For Makoto, this embarassing situation becomes reality when he and two classmates are inadvertently transported to a magical world full of castles, royalty, and giant armored bugs. There, he is mistaken for Fatora, a missing princess, and quickly becomes entangled in a seven day quest to find her, all the while fending off female advances and trying to clear his name!
As a child, Inaho always loved listening to stories of her grandmother's immortality -- gained from a strange device known as the O-part. As a young adult, Inaho is finally ready to fulfill her dream: to find the O-part and gain immortality, just like her grandmother! But where can the O-part be found? Fortunately for Inaho, she has made a blood-pact with Mosquiton, a 1/4th vampire with a knack for servitude, and a nose for trouble. Joined by Mosquiton's ex-wife and two cohorts, the search for the O-part begins! That is, if the world isn't destroyed first...