Familiar Spirit of the Demon Lord

Today is the 2400th birthday of the prince of the demon's realm (you). - You make a lot of effort in a demon summoning ritual in order to have - your own familiar spirit, but a human girl is summoned instead of a demon...!? - Even though you are the expected next demon lord, people may underestimate - your magic ability... You have to prove your ability by making the human girl into a demon!