In a world where aptitude for magic is determined by a crest. At the age of seven, Alec, the sixth prince of the sacred Luxian Empire, was given a crest of [Dark Magic], which is said to turn him into a demon as soon as he uses it. Scorned by those around him, Alec became a shut-in in the palace, and in the last days of his life, he used [Dark Magic], which he had never used before, in the hope of getting a good glimpse of it. However, Alec's crest was actually a special one that allowed him to use [Dark Magic] without having his body taken over by a demon! He died as he was - but when he woke up, he was back to his childhood! Reverting back to his seven-year-old self, Alec uses [Dark Magic] to turn all kinds of demons into his dependents, and together with his strongest companions, he builds an ideal country...!