Rivera

Biography
Corporal Rivera is a Learning Disabled Marine who served in Makin and then died. He somehow came back to life because of his magic katana (the reason he was allowed to fight in the war). He is seen when Miller doesn't follow Sullivan and Roebuck but instead goes on the platform with Denny, Snider, and Slayback at the beginning. Near the end of the platform you can see a Japanese soldier and a Marine fighting. If you took the right with Sullivan and Roebuck, Rivera would die. But taking the left gives you the chance to kill the Japanese soldier. Rivera will try to find cover but can be killed while doing this. If he lives than he'll be with the others whom are fighting the MG nest. After that and he makes it through all that and the banzai attack then he'll die anyway with Rooker and Lozano at the 2nd gunfight. We expect him to use his katana and come back to life in the next Call of Duty:

Strangely if Rivera and Lozano live through the MG nest than Denny will die for no reason like Ryan would. Rivera holds an M1 Thompson. Also if Lozano and/or Rivera live (it can be both or only one of the two) Rooker will die at the 2nd gunfight by being shot instead of the ambush where he is stabbed. It all seems to be a bunch of confusing garbage.

Rivera may be another member of the recon team and was interrogated. If that's the case then he probably ran towards the Marines, hearing the rescue mission but a Japanese soldier caught up with him and resulted in the fight you can see.