"Death Times Three"
Story takes place after Catalyst: Agents of Change #1.
Grace only appears in flashback. Mecha appears in a one panel cameo.
*Out of the Vortex: Death Times Three brings yet more bloodshed to planet earth, as the next Reaver Swarm agents arrive -- three more Destroyers who struggle to unite their forces into a single deadly force before the alien from the Vortex can stop them! Whether they succeed or not might depend on a wild card up the alien's sleeve: enter David MacRae and the mysterious entity, Zero! The Destroyers are more than a match even for the kick-butt adolescent giant, Hero Zero, until Zero reveals a new power David has never suspected! *Source: darkhorse.com