Little is known about Grencia Mars' past. When he deployed during the Titan War he was stationed in the same company as Vicious. During this time Gren admired Vicious as a soldier. He was given a music box mechanism from Vicious that played the song Julia. Unknown to Gren, this music box contained a solar transmitter. On Callisto he lived at the Orlando Apartments, a blue building, in a town completely devoid of women. He played the saxophone at the Blue Crow where only two women ever patronized: Julia and Faye Valentine.
At the drug deal Vicious attempted to kill Gren with a suitcase bomb and later shot Gren's zipcraft to the ground. Gren managed to slip the music box, with its solar transmitter, onto Vicious' ship that caused an explosion to his wing. Vicious managed to escape, but Gren suffered fatal internal injuries. In his last moments, he requested Spike to power up his engines so he could go to - and rest in peace on - Titan. He died on the journey.