If you're looking for manga similar to High School DxD EX (Light Novel), you might like these titles.
"Hey, you said you wanted a little sister, right?" First year highschool student, Toujo Basara, was suddenly asked this question by his father, and he fell into a state of panic. On top of that, the eccentric father told him that he will be getting remarried. He then departed overseas after bringing Basara two beautiful step-sisters. But Mio and Maria's true forms are actually a newbie Demon Lord and a succubus!? Basara was almost forced into a master and servant contract with Mio, but a "reversed" contract was formed by mistake, and Basara is now the master!? Moreover, Basara is being hit by ecchi situations one after another due to the contract, but Mio's life is being pursued by other demon tribes and hero tribes!
Narrates the story of Kyuuki, a strong, proud fox demon who recently woke up and needs a host and Kamishiro Shin, a normal would be high school student if it wouldn't be for "his ability" and for the fact that he got a hold of the black Grimoire that controls Kyuuki's existence. Shin is bound to the book as long as he is alive, thus not only he can't sever his connection to Kyuuki; but those who want the book's power are bound to come after his hide regardless of time and place.
In a world where everyone has the ability to use magic, Kazuki Shikimori -a descendant of the world’s greatest magicians is now being sought after by girls -for his genes!! Can he stay alive? Because these girls will seek his help and cause his limited magic to drop to zero and turn him to dust.