Image: Sucker Punch Productions / PlayStationOfficial screenshot from Sucker Punch Productions / PlayStation.
Dying Embers is an Act 2 story trophy. It unlocks when you finish A Reckoning in Blood, the tale where you strike at Fort Koyasan before the assault on Castle Shimura.
Finish the three Act 2 objectives first. Meet Lord Shimura at his camp, then head to Fort Koyasan and clear it. The trophy pops when the tale ends.
The traitors are Ryuzo and the Straw Hats holding Fort Koyasan. The fallen friend is Taka, killed by the Khan earlier in the story.