If you're looking for manga similar to Demon Diary, you might like these titles. All recommendations are made by Anime-Planet users like you!
Ishuca is a man who has been told he is going to die. So as to not disturb anyone, he travels to a remote cave where he encounters an ancient demon known as Blood; trapped in the ice for centuries, Blood is about to eat Ishuca when the man offers his body to the demon. While Ishuca then dies naturally, Blood is so touched by the man's kindness that he inadvertently revives him with his tears. Together, the two set off on a grand adventure and unintentionally try to breach the rift between humans and demons; for they are not as different as they may seem to be.
Both extremely cute centering around the love of two male characters. Both are fantasies with bunches of humor and "OmiGod That's so cute!" moments abound. Both main characters fall in love with a demon, but the plots are entirely different, so it's not like reading the exact same story either.
Bot manga centres around relationship between former "ordinary" human and demon. In both there is some kind of journey where "human" learns about demon world.
Koori no mamono has more action and is more thrilling and might brign you on werge of crying (which i wouldn't say about DD), but it's still so sweet...
Demon Diary, on contrary, is more cute :3
Artwork is really great and if you like bishies, your heart will squee with joy :)
Both anime are about demon's that have to finish off what they started and get into a relationship in some form. Hitomi kara Destiny is shoujo and short where Demon Diary is shounen-ai and more fleshed out because it is longer, but if you enjoyed one you'll like the other as well.