If you're looking for anime similar to High School DxD, you might like these titles.
At a school full of geniuses from varying fields of study, Taketo Akutagawa has a special – albeit different – genius as well: writing harem novels. Now amongst the other geniuses, he aims win the interclass competition and be recognized as the world’s greatest harem writer
After saving a fairy-tale kingdom, Akatsuki returns to the real world with his prize—Myuu, the busty daughter of the defeated Demon King. It’s one hell of a happy ending until they’re forced to enroll at a school for magic users. There, Akatsuki can’t keep his hands off the girls, Myuu’s constantly ballooning measurements make her a walking wardrobe malfunction, and it seems like someone is always plotting against them.
Taketo and the gang find themselves stranded on an island. Little do they know this proves to be a treasure-trove of material for Taketo's unique pornographic literary skills.
Heavens Library & Crimson Lord brings back Arata, Lilith and the rest of the Trinity Seven to face off against the greatest enemy in the history of the Trinity Seven; Lilith's own father, who is revealed to be the strongest Demon Lord who challenges Arata who is now a Demon Lord candidate.
What’s the best way to celebrate a birthday? Well, to the succubus Maria, there’s only one thing to do—get Mio and Basara to hook up! Using the guise of Mio’s birthday, and a lust spell, she’s determined to have the perfect setup for a sexy celebration.