From Halopedia, the Halo wiki
During 2525, Mason was in ODST boot camp with Gage Yevgenny and Kiko in a squad led by Felicia Sanderson. Their training was accelerated following the emergence of the Covenant threat, and an altercation between Gage and Felicia led to Felicia being moved to another squad and replaced by Rahud. Mason made his first combat jump onto the colony of Hat Yai three years after he finished training.
Mason died in Gage's arms on Asmara after a Sangheili speared him along with ten other ODSTs with an Energy Sword before Gage got off a near point-blank shot with a missile launcher. As Yevgenny would later recount: I found Mason lying among the debris; I could smell his seared flesh. He looked up at me with glassy eyes and asked for his mother, then coughed up blood and just...stopped being.
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