- Izabella's situation, she's 14, lost her entire family in the battle of Chicago 6-8 years ago, and has been homeless since at least the age of 8 maybe even younger.
- Due to that it seems that she identifies more with the Autobots than with her fellow humans, with Cade being the only human character she gets close to and he too seems to prefer Autobots to humans at this point in his life.
- Bumblebee being forced to fight Optimus Prime, while the latter pins him and is about to deliver the killing blow is heartwrenching to watch, especially when you consider the previous movie hinted that Optimus was like a Parental Substitute to the young Autobot.
- The way Optimus says "Forgive me..." in a sorrowful tone. He's not in control of himself and is forced to fight and possibly kill Bumblebee. The fearful expressions and Bee and Cade's faces make it even more heartwrenching.
- Earlier, we get a spot of a group of kids wandering a war-torn part of a city. The war with the Autobots and the Decepticons has left many scars on Earth and its people.
- Despite everything that's happened in the past four movies, the relationship between Transformers and humanity has not improved. If anything, it actually seems worse than before.
- Seeing Optimus float in space, lifeless and worn, is bound to tug your heartstrings.
- Sqweeks...just Sqweeks. Remember how Bumblebee can't talk because of a broken voice processor? Well this guy's so broken he can't even transform!
- Izabella's desperately begging Canopy (who has been struck by a missile) to get back up.
- Megatron finds Starscream's severed head and seems to mourn him. Apparently he really did care for at least one of his followers, despite his abusive treatment of him. It also implies that Megs never knew of Starscream's demise.
- Optimus and Megatron are fighting. During said fight Megatron practically screams with a sorrowful tone "We were brothers once!" to Optimus. A heartwrenching reminder that despite everything else these two were once close allies.
- Optimus solemly responds with "Once...".
- Merlin's plea to the Knights of Iacon for aid against the Saxons in the beginning is one as he begs them not to let his world die as their world did. He admits during it that he's a fraud who's deceived others his whole life and would give up nearly everything including drink and money for one moment to make our world better.
- Sir Edmond's death. Even Cogman admits that seeing the Folgans pass away multiple times was his hardest job in his life. Despite this, Sir Edmond tells him to carry on before he dies. Cogman even slates that Sir Edmond was "the coolest".
Tear Jerker / Transformers: The Last Knight