Soul Star
The Soul Star is an alien artifact that acts as the symbol of the Aeons and, according to the Fugitoid, contains the power of life itself. A small crystal fragment of it was in the possession of April O'Neil, who wears it around her neck as a necklace and uses it to help focus her psychic powers throughout most of Season 4. Over time, it has also had a strong impact on April's emotions, and she has gradually become so attached and protective of it that she will instantly snap and become hostile to anyone who tries to touch it (as shown when she slapped Donatello's hand away when he reach out and asked to look at it).