If you're looking for manga similar to High School DxD (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!
Raul Chaser wants to be the Hero famed for defeating the Demon Lord - at least, that used to be his dream, until another warrior beat him to the punch! With peace now restored and all Heroes out of commission, Raul reluctantly gets a job at Leon, a small store that sells magical commodities. Compared to slaying demons, Raul’s new life of greeting customers and working the register is uneventful at best - that is, until Fino Bloodstone, the Demon Lord’s busty daughter, is suddenly hired at the stop! Raul now faces a challenge more difficult than vanquishing her father: teaching the clumsy and ill-mannered Fino how to become a respectable employee, while simultaneously fending off tentacle monsters and putting up with pervy regulars’ skirt-flipping antics!
As a regular high school student, Haoyi Jiang prefers to stay out of troubles, but troubles find him in the form of female classmates suddenly falling in love with him!
The story begins with Blaze — a weapon that is the manifestation of a human's soul. Thor Kokonoe happens to be qualified for this, but for some reason his Blaze is not a weapon, but a shield. Moreover, he enrolled in a school that teaches combat skills, and thanks to the school's Duo partner system, he ends up living with a beautiful silver-haired girl.
Ohyama Takeru happily enrolls in a co-ed school that didn't require any entrance exams and has hostels to boot... Only to find out that there's more to the school than he thought!
Youtarou Hanafusa is a descendent of the “Knights of the World.” With the Knight’s Code of Chivalry hammered into him since childhood, Youtarou cannot stop himself from saving damsels in distress. He wears a mask, and is known on the street as “Knight Lancer” but he has always kept his identity a secret. While on an outing, Yotaro saves a 6-year-old girl, Makio Kidouin, the only child of a powerful business tycoon. When Youtarou discovers that Makio leads a lonely life in a huge estate, he resolves to protect her. He and his friends disguise themselves as lodgers and move into her mansion.
High schooler Takuma Akutsu is terrified of human contact and just wants to live a quite life. Too bad he doesn't have a choice in the matter when nine Valkyrie sisters come barging into his home! They've tasked him with raising their level to fight off the monsters threatening humanity--and how will he do that, exactly...? By gettin' down & dirty to the max!!!