The series is set in a world where magic exists and has been utilized as a technology for nearly a century. Rather than casting spells with chants or other traditional forms of spellcasting, mages use a Casting Assistant Device, better known as a CAD. Mages infuse the CAD with psions or thought particles (a substance-less particle and psychic phenomenon) while the CAD itself provides an activation sequence, which is then used to construct a ritual in order to invoke the magic. This magic ritual targets the Idea, the platform on which Eidos are recorded. Eidos refers to a form of information that is attached to a phenomenon. Modern magic uses false signals to manipulate the Eidos of a target, which in turn modifies the phenomenon and causes physical changes in the real world.
In 2095, Tatsuya Shiba and his sister Miyuki Shiba are new students enrolling at the Private Magic University Affiliated High School (First High School). Students are ranked according to their test scores: students with the best grades are enrolled in the Course 1 curriculum, while those with poorer scores are enrolled in Course 2. These streams are known colloquially (and against school policy) as "Bloom" and "Weed". Miyuki topped the entrance exams and is selected to be the first years' representative, while Tatsuya is placed in Course 2 due to his low practical test scores, despite scoring highest in the written/theoretical portion of the exams.