In both instances Alloy is Tasked with a choice. Will you have mercy on Olin? Will you accept Nil’s duel to the death?
Saving Olin and deciding not to duel Nil to the death will allow these guys to appear at the end to help with the final fight. choosing weather or not to kill Olin or not duel Nil will have no effect on the trophy All Allies Joined. If you choose to kill these guys the only reward is a quick cut scene.