Rebellion is a Devil Arm created from Sparda himself and passed down to his son; Dante. It is a Weapon centered around its ability to cast Mystical Dark Magic that takes the form of Dark Flames.
It is also a shapeshifting Blade that changes shape depending on its User's emotions and connection to the Devil Arm itself, it has a strong bond with Dante due to its heritage as apart of his father, Sparda.
The Rebellion was a Devil Arm split from Dark Knight Sparda when he felt he was getting too powerful. To avoid becoming a superpower he weakened himself by splitting himself into three entities- Sparda himself and the Swords of Sparda; The Rebellion and The Yamato. He left them as keepsakes to his sons; Danta and Vergil who would later take them up as weapons and discover their power.
The Rebellions most basic power is its dark magic derived from Sparda allowing it to cast Dark Magic. This magic currently only includes Dark Fire and a Dark Shield. The Rebellion has many forms but it normally takes a dark and demonic form with the color scheme of black and purple with a trademark eye. It increases its power with each shape depending on its connection with its user's emotions.