This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / Transformers Cybertron
Transformers Cybertron with Vector Prime disappearing after reversing time to let the Autobots fight Galvatron after the space bridge at Gigantion was destroyed.
What really hammers it home is Bud, the youngest of the kids being so deep in denial and grief that he couldn't even comprehend why everyone else was crying their eyes out at first, and then he completely breaks down too.
Some time later, when the team returns to Earth, and they visit the old base, Safeguard, Vector Prime's mini-con partner, looks up at the launchpad and imagines his old friend taking off.