Tanarotte Unthirteen

Described as being "Unknown". A young, well-endowed, familiar that was summoned by Takuto but it is unknown if she is a god or a demon. Her magical power is over 100,000, divinity power 5,000, offensive power 5,000 and defensive power 78,000 and is physically strong as well, able to hold off a small army of Golem units with only a single hand. When first summoned she was running on pure animal-like instincts and tended to act like an affectionate cat around Takuto (only saying Myu, clinging to him while being completely naked, and licking his cheek). It wasn't till Takuto gave her her name (as she reminded him of a cat he once had named Tanarotte) that she calmed down and was able to talk.

She is shown to have a genuine affection towards Takuto and treats her Familiar service to him as if they were a newly married couple, but her personality resembles that of an energetic child. It is later revealed that Tanarotte has the power to 'evolve' into either a god or a demon. Both the gods and demons are concerned by this as it could shift the already delicate balance between light and darkness to one side. A running gag is every time she is in an ecchi scene, she is replaced with a claymation version for the viewers. In episode 4 she becomes a student in the same school as Takuto. -Source: Wikipedia