それじゃあ吉田くん!

King Dark Fleet is bored of ruling the Demon World and so he appoints a successor by the name of Yoshida. The demons are thrown into a rage when they realize that this Yoshida is a human boy. Cute demons begin to enter our world through a magic mirror, bent on killing Yoshida and taking the throne for themselves. Of course, the young boy has no idea of his new kingship and only has his limited magical powers to protect himself and his friend, Ageha.