The nobles of Halkeginia are magicians known as "mages" or "magi", and must use a wand or a staff to cast spells. Not all magi are nobles, as some have been forcibly demoted or given up their nobility and use their magic for thievery or to work as mercenaries. There are four primary magic elements: Ignis (Fire), Aqua (Water), Ventus (Air), and Terra (Earth). Magi have an affinity to one of those elements. There is a fifth element, the legendary lost branch of element, known as void. Magi can combine different magical elements or even stack the same element on top of itself to make spells more powerful. The power of a mage is determined by how many elements he or she can combine. There are four ranks of magician based upon this factor. Those who cannot combine any element together have the first rank, which is symbolized as a dot. Most magic students are in this class.

Louise Françoise Le Blanc de La Vallière is a member of the nobility who is terrible at magic, as her attempts usually result in an explosion. She is nicknamed "Louise the Zero" by her classmates, due to her inability to use any of the four magic elements. Early in the school year at the Tristain Academy of Magic, the second year students perform a special ritual where they summon their familiar, which serves as their eternal companion, protector and partner, and is usually some sort of magical creature. But Louise summons you an ordinary teenage boy from Japan, leaving her totally humiliated. Due to the sacredness of the ritual, Louise reluctantly accepts you as her familiar, but proceeds to treat you as any other familiar, only worse: making you wash her clothes and sleep on a bed of hay, and whipping you with a riding crop whenever you upsets her. The adventures of Louise and you as they help their classmates and friends, while occasionally blundering into situations where they risk their lives to save one another. As you and Louise's friendship grows and they start to work together, they ultimately fall in love with each other.