Yaoguai Mingdan

Boy gets mixed in magical/supernatural fights, obtaining a harem on the way. Both series try to mix fanservice and drama, though High School DxD has much more fanservice. 

Chinese web animations about a guy kinda acquiring a harem just by existing. Both are comedies and have a quirky kind of humor that is typical for chinese anime. 

Chinese series <3. We are talking about two really different stories, but at the same time very similar with the whole theme of reincarnation and demons, etc. Huyao is translated into Japanese, Yagouai is not. but leaving aside that I think that if you liked one you'll like the other (Huyao is more comedy / romance and Yagouai is more drama / romance) 

Both Chinese animation Both MCS have past they dont remember both MCS are surrounded by beautiful women to help them get stronger.  

Both anime are anime about fighting with magic & lewd humor with harem antics