SPARTAN-500

Born in 2525, Marrissa was two when a rogue ONI Section III officer killed her parents and abducted her. He did it to two other children, and she writhed under the man. The officer trained Maria and the other two children in the art of warfare, in hopes he might make them SPARTANs one day. However, six years into training, Section 0 of ONI sent in SPARTAN-144 to kill the man for treason. 144 Soon found the three SPARTANs, and brought them back to Reach. Once there, they received more training, then were augmented and turned into Section 0 enforcers. However, they eventually shifted to the front. In 2552, the makeshift SPARTANs were transported to Reach and given MJOLNIR Mk. 5, but the planet was attacked by the Covenant. The SPARTANs made their way onto the Marathon Class Cruiser Valley Forge, and then were transported out of the system when the ship fled with the rest of Taskforce Avenger. 
They tried fleeing to the Eagle Nebula, so, that they could return to Earth and warn of Reach's destruction, but they were engaged by Covenant ships. After Covenant troops began boarding, the trio of SPARTANs were dispatched to fight off the enemy. They fought for several minutes, but it soon became clear that the ship was going to be destroyed. They fled aboard one of the alien boarding craft. Their craft was heavily damaged when the Valley Forge rammed a Covenant Supercarrier, and for some time, they were stranded. 
They drifted for a little until theUNSC Apollo and the UNSC Vulcan's Hammer found them. They then joined up with the Apollo and hitched a ride to Kamos System. There, they redevoused with the Deadalis and went down to the planet to try and find ammunition and supplies, and discovered a UNSC testing facility. They found the supplies they were looking for, but also found Mk. VI Mjolnir armor. They were fitted for the armor and were about to move out when a covenant ship entered the system and launched an invasion. During the ensuing battle, Marrissa was killed.