Elite Neco Corps

The Neco Arcs summoned by Neco Arc. The GCV's only military unit.
It is a self-defense force composed solely of specially chosen Neco Arcs whose overflowing savage nature, excellent physical ability, and unmatched intelligence cannot be controlled. These chosen few are known as Abaddon's Beret, and are the envy of all the Neco Arcs.
Of course, that's completely unrelated to its power as a technique. There is a high degree of randomness involved, so it's really only useful as a provocation. Probably, this was done in order to faithfully translate the idea that even Neco Arc cannot control the Neco Arcs into game mechanics.
Also, recently there have been rumors swirling about a Dark Chaos Corps, but…?

MB Act Cadenza PS2 Manual: Tsukihime Dictionary