Diana is a goddess living in Tenri's body, and she's got that classic tsundere thing going on mixed with an innocent, pure-hearted side. You can always tell when she's taken control because a halo literally appears above Tenri's head. She and her sisters—collectively known as the "Sisters of Jupiter"—made a huge sacrifice ages ago to seal away the Old Hell, which is pretty much the defining event of her existence.
As a heavenly being, Diana runs on love; it's basically her fuel source and the only thing that lets her grow stronger. Knowing this, she decides the logical solution is to ask Keima to marry Tenri. Yeah, that's her approach to powering up.
Content compiled by AnimeList.moe from publicly available sources.
