Seeing the bright, friendly and enthusiastic Bill Randa in this series makes the bitter and ruthless Randa we see in Kong: Skull Island, and his demise in that film, much more tragic.
He shows he's regretful for all the things he cost Hiroshi which he feels he can never replace.
There's something really poignant about seeing a parent prepare to face their possible death earnestly believing that their own child won't be too upset at losing them.
What makes this so much worse is that Cate manages to get a few kids out, and it looks like she just might make it. This is before a piece of debris knocks away the last chunk of asphalt under the bus, thanks to Godzilla. You can hear all those kids screaming as the bus falls off the bridge.
The fact that Godzilla didn't even mean to kill those kids. It was all a tragic accident instigated by his panicked response to the military's even more panicked strike on him. Really, no side is truly innocent or guilty in this situation.
Pretty much everything we see here about Cate's experiences on G-Day and her relationship with her Disappeared Dad.
The fact that her father left Cate and her mother in the immediate aftermath G-Day makes it even worse. Not only was she traumatized by the death of the kids on the bus but also associates that day with her father leaving her and mother.
Cates very clear PTSD from G-Day. An evacuation drill for Godzilla has her flying into a straight up panic attack until Kentaro’s mother manages to calm her down with a Cooldown Hug and words of comfort.
Keiko's frankly horrific demise at the claws of the newborn Endoswarmers paints all of her subsequent appearances in a tragic light. Seeing her grow closer to Shaw and especially Bill, knowing that it will end with her dying like THAT, can make her scenes hard to sit through without the Dramatic Irony sinking in.
At least, until "Axis Mundi", where we learn that she survived the encounter. But even THAT carries a bit of tragedy. Imagine how she'll be feeling knowing that the love of her life corrupted their purpose and died horribly because of it.
"Secrets and Lies"
Even though Keiko is officially part of an American-made organization, it doesn't stop her more narrow-minded bigoted superiors from treating her differently due to her Japanese heritage.
Then, there's Randa and Keiko's horror to discover the military are planning to use the uranium they requested to kill Godzilla.
Just imagine from Keiko's point-of-view. She witnessed the devastation nukes affected her country and her people and now, one is being used to kill an innocent creature whose only alleged crime is for simply existing. No wonder she tries to stop the operation and breaks down when Godzilla is seemingly killed.
"The Way Out"
Cate and Caroline's heartfelt argument, where it's revealed to the audience that after G-Day, Cate was so depressed over the deaths of her schoolkids in the falling bus that she spent most of her days locked in her room in her and her mother's FEMA trailer and wasting away, for an entire year. When Caroline recalls that Cate wouldn't reach out to any support groups, Cate tearfully snaps, "Because pottery classes aren't going to bring my kids back from the dead!"
Caroline meanwhile admits that she suspected Hiroshi had been hiding an affair when she sent Cate to investigate his old Tokyo office, and that she was so desperate to try something to shake her daughter out of her depression that she sent Cate to find out the ugly potential truth herself because nothing else was helping Cate.
"Terrifying Miracles"
Duvall reveals that she is the sister of Sandra Brody, who died in the Janjira nuclear power plant in Godzilla (2014). So not only did her sister die in the power plant, her brother-in-law died due to injuries caused by the male Muto's awakening, and her nephew Ford and his family are her only surviving relatives.
"Will The Real May Please Stand Up?"
Cora had to flee a loving home full of relatives who loved and adored her, including her sister and mother, because of her cyber-attack on AET forcing her to go on the run.
The Frost Vark’s death evoked this reaction for several fans: “Maurice” as some called him was just an animal (albeit a dangerous one) who was only following his instincts, and during Shaw’s attack, was simply trying to chase intruders from his territory. As he’s sucked into the collapsing Hollow Earth vortex, the poor Titan can clearly be seen thrashing in terror and confusion before the explosion kills him.
"Birthright"
May/Cora's family just got her back, when she falls into the Hollow Earth and is believed dead at most just days later. Whereas she's still alive, the final episode reveals that she was missing for two years.
''Axis Mundi"
Lee reveals to Hiroshi that his mission to the Hollow Earth went south very quickly. One of his crewmates died on arrival, his female colleague was shocked to death, and another member was accosted by a monster. Hiroshi coldly dismisses his clams and returns his pocket knife, which explains Lee's sour mood in the present and his agenda to help Godzilla.
The reason why Hiroshi sent Lee to the Monarch retirement home? "I buried that family in three empty boxes a long time ago". While he's glad he reunited with Lee, he had to make a funeral for his parents and Lee when he thought Lee had died, and he didn't want to continue where his parents left off because he didn't want to lose his only family he has left. This becomes a Dramatic Irony when his own mother is actually alive by the episode's end.
When Kentaro wakes up, Verdugo tells him Cate, May, and Lee didn't survive (they actually did, but Monarch doesn't know that). He visibly mourns even as he returns home. When he sees his father, he calls him out on for having a Secret Other Family, and Cate didn't survive. Hiroshi doesn't take the news well, and collapses on his knees when he realizes his secrecy destroyed his own family.
"Beyond Logic"
Lee's reunion with Keiko. Keiko was trapped in Hollow Earth for 57 days, but so much time passed that she didn't realize Lee entered it in 1962. Until Keiko meets Lee and realized how old he's gotten. So much time had passed for her that her husband died, and Hiroshi is already an adult. Because she also finds out that Cate is her granddaughter that she feels she doesn't belong on the surface anymore.
Lee's Heroic Sacrifice. Up to this point, he thought he was the only original Monarch member left, and he finally makes a tearful reunion with Keiko. As Godzilla fights the Ion Dragon, Lee is holding on Keiko's hands, and lets go so her, Cate, and May would survive.
Cate finally reunites with Hiroshi after he thought she had died, but then he finally see his mother, whom he hasn't seen in decades after she disappeared in Hollow Earth.
