Mr Miyagi's entire backstory, from leaving the one he loved to leave a death fight, to marrying but forced to go to war thanks to racial prejudices, only to lose his wife and unborn baby to childbirth while in combat.
Miyagi's father's death scene, the last thing he wants from both Miyagi and Sato is to not fight each other. And Sato, who is a massive Jerk Ass, can't bring himself to say no.
Miyagi trying to make peace with Sato. He asks an Armor-Piercing Question to his old friend when he ruthlessly rebuffs attempts. It's a powerful tear jerker because you can see both Miyagi's concern and Sato's pain from his long belief that his old friend hurt him. It is also the first and only time Miyagi talks to anyone without his trademark broken english or referring to himself in third person.
Miyagi: What has happened to you?!
The torment Daniel goes through in the first movie: he is beat up at beach party, losing the friends he just made. Then he's banned from soccer after picking a fight with a guy who tripped him. In culminates in a savage beating from Johnny and his friends, that Mr. Miyagi has to save him from.
The car smashing scene. Made worse by the fact that he caused the car wreck that he's reliving that killed his wife and child.
"Every year, I fix the car. Still fix nothing."
Han talking about how he can't remember what he and his wife were arguing about just before the crash and how he hopes that it had been about something important.
The moment where Dre is injured and Han runs onto the arena floor comes surprisingly close.
Dre's homemade growth chart in Detriot, with a mark for the day his father died.