Also known as: ダークオーブ
An item from the third Mahou Shoujo Madoka Magica movie.
Note: Major Spoiler Warning!
The Dark Orb is the Soul Gem of Homura after it gets corrupted with love rather than grief (which would result in a Grief Seed). It takes the form of a black crown and shines in impossible colours. It enables her to transform into Akuma Homura, the Demon to Ultimate Madoka's Angel.