Raven Suits are highly advanced and powerful Anti-Beast battle suits created by Ray Nelson, who was the Deputy Director of the Central Order's R&D department, but was fired from Knight Order after being set up Miliaria. (AE2 - Ch13)
After the defeat of EX-Type Zero Hyperion, its AAA-Class Red Sidereal Weapon Mysteltein was recovered and studied in order to use its power for the spears wielded by the Raven Units, known as the Double Zero Spears.
These spears are the most powerful weapon of the Raven units and they replace the reliance on AB Swords, which can only be acquired from the Knights. The spears are "mediators" that convey the power of Mysteltein to the target. The Double Zero Spears have the same erosion ability, but it's much weaker and requires direct contact with the target.
However, during use the resonant structure holding Mysteltein must be within a certain range for it to operate. This is a major drawback in addition to the fact that the resonant structure has no barrier shield and has low mobility.
Speaking about Sion being subdued by these spears, "There's no point. That's our ace in the hole to substitute the AB Element. She won't be able to resist. Those spears are just replicas... ...that only resonate the original. And the curse that enables the resonance comes from... Mysteltein. The cursed piece of wood from the enemy." Robert Nelson, (AE2 - Ch30)