Welsper

From OMGWiki

Velsper is a demon, who is in a doublet with Belldandy. However, he cursed himself to remain in child form in exchange for remembering his encounter with Belldandy. The curse could only be broken if Belldandy speaks his name. As Belldandy's memory was wiped of their meeting, this would prove difficult.

The bad thing about his curse was that his power was quickly growing, and couldn't be contained within his child form. He had to get the curse to break if he was to live... and if Belldandy was to live.

Well, in the end, Belldandy finally speaks his name. However, Welsper then hacked into Yggdrasil, and was punished afterwards by being reincarnated into a cat.

Still, though, he cursed himself AGAIN in order to remember everything and keep his intelligence. So he still lounged around at Tarikihongan in cat form, but Hild found him and turned him into a girl. Also, after Welsper had the Familiar transferred over to him, he got white spots. In order to remove those white spots, he had to name his Demon Servant. After he did, he returned to normal.