Welcome to Demon's School Iruma-kun and Arianna-san

Arianna is the unknown daughter of the high ranking demon who is the best friend and right hand of the missing demon king Delkira. When her father was summoned in the human world by greedy human who wished for wealth, he met her mother there who is he half-sister of the human who summoned him and is the one that the human had wanted to sacrifice but the demon had saved her and punished the other human by making him an idiot who can only think the same as a 5 years old human child. After being saved, her mother and father got to know each other and fell in love and later conceived her but their love story ended when the demon was found by his enemy and her father could only sacrifice himself as he did his best to erase all those that knew about her and her mother and finally died when her almost dead last enemy tried to kill her mother. Before dying, her father had used all his remaining mana and soul to give his power to her so that when she do return to the demon world where she i rightfully belong then she will have enough power to survive. Before dying, he also called hi trusted friend Sullivan that should he and her mother died then he must adopt her and return her to the demon world to which the demon agreed. And just like that, Arianna began her journey to the demon world along with her unfortunate best friend Suzuki Iruma.