If you liked the Sora no Otoshimono anime, the Anime-Planet community thinks you'd like:
While trying to protect a wooden relic, high school student Yuuri Mito summons the Goddess Kikuramikami no Hime in the form of a sweet, affectionate child; she begins to live with him, taking the name Mashiro. Yuuri promises to marry her when she grows up, which unfortunately for him happens overnight! However, they soon have bigger things to worry about, as the relic is accidentally destroyed, unleashing the Tayutai, a human-hating race of monsters. Along with Yuuri's childhood friend Ameri, his step-sister Yumina and Mifuyu - an honour student at Flawless Girls' Academy - Yuuri and Mashiro must step up to fight the Tayutai, protect the world, and even learn about underwear!
Both of these series have a random girl with super powers show up out of nowhere and are willing to do almost anything for a random guy, making their childhood friend jealous. If you like one of these supernatural/ecchi series, you'll likely enjoy the other.