From Halopedia, the Halo wiki
In a ground engagement during the Harvest campaign on February 4, 2531, at a Methane refinery near the relic the Covenant found, this Spartan (with no backup) engaged 25 Covenant soldiers. The Spartan killed seven Covenant soldiers but was quickly killed by the Sangheili Ustaf 'Nbekee with a Needler. As a war prize, the Unggoy under 'Nbekee's command were allowed to play games with the Spartan's helmet.
This Spartan's only appearance is in a brief in-game vignette on the now-defunct official Halo Wars viral website, in which the soldier's identity and gender go unmentioned.
It is possible that this Spartan is Joseph-122, as only his and Keiichi's status following the Harvest campaign remain unaccounted for: Three Spartans had died by that time (two by suicide and one in combat) while the remaining 28 have been named and are known to have survived the Harvest campaign.
It is unlikely that this Spartan is Keiichi-047 because despite Keiichi's status being MIA, he was seen fighting later on in the same day in a sunny period, while the unidentified Spartan was seen fighting during a dark period when Alpha Base was most likely running.