Everything about college student Amamiya Yuuhi is average: grades, looks and his blasé outlook on life. So what happens when he awakens one day to a talking lizard, who informs him that there is a gigantic hammer in outer space, poised to split the Earth into pieces, and requests his allegiance in the fight against the forces of evil? Pretend it never happened! Unfortunately for Yuuhi, a little bit of coercion in the form of a super-powered princess prevents him from returning to his mediocre life-as-usual. In the adventure of his lifetime, Yuuhi will join forces with the unpredictable princess and seek out a motley crew of companions to fight back against an evil mage and his horrifyingly powerful homunculus before the Biscuit Hammer destroys the planet!

Jun Shirasaki and the Jinguuji sisters are childhood friends and neighbors. When Jun's first girlfriend, the older sister Ryuumi, breaks up with him, she says something that complicates the three people's relationship, their first loves, and their romance—?