TFA: Deals with Our Devils, Chapter 9: Departure
Ultra-magnus and sentinel prime had seen a lot in their days, but nothing could have prepared them for what they saw the recently downed autobot did. Surviving after what would kill most bots was scary enough but bursting into flames and sending megatron sky high was terrifying.
The energon covered optimus let go of Blitzwing spark from his jaws letting it fall to the rubble with a, clang! noise. Like a hungry predator that was done feeding. Fresh from the kill.
Sentinel noticed sharp teeth like abrasions like an organics jaws that subsided in Optimus's mouth plate when he let go of Blitzwing's spark chamber.
"Optimus"? Sari said in shock.
Optimus didn't reply. He simply stood his dark form upright looking onwards in the distance. Then with a gust of wind that went by he started walking away, without saying anything. What could be said. He didn't look back as sentinel and ultra magnus or at his friends as they cried for him to stop, but kept on walking away. With every step he took he reflected on what he did to a bot he never would have thought of before he died.
The shouting was louder now, but he persisted forward, even when ultra magnus demanded he turn around and jazz had to hold his friends back that tried to move he kept moving forward.
Then as the construction robots and police started to show up optimus walked behind a dark corner as he disappeared leaving his scared friends and comrades behind.