An idea for a Halo/Marathon story

Reading some more of Finishing the Fight by Red Mage 04 (Halo/Forgotten Realms crossover) inspired me to doodle some Halo stuff (regardless of how frustrating its armours are to draw) and gave me an idea for a different crossover, which I'm writing notes for here so that I don't forget them.

( I may have cheated with the ending of Halo 3... )