I kind of always felt bad in Halo Wars 2 when my Marine squad was low on health and the Sergeant would say "We've lost a few good men sir...." It's almost as if they knew you were sending them to their deaths. (Reminder the more health you lose, the less marines are in a Squad)
Another is the Marines in Halo 2, "My little brother was on Reach!" all while shooting the dead Elites.
When you crash on instalation 04 and all the marines are dead, bro; they were new soldiers, some of them might had lives and some were excited for see the chief in person, but they died in a crash...
And main characters...hmmmm, may be Johnsson or Kat.