Keiko's extremely distressed and emotional reaction to the U.S. military attempting to kill Godzilla with an atom bomb can seem a little... over the top to say the least, considering that she lacks the Serizawas' history with Godzilla and has no way of knowing whether Godzilla is a protector or a hostile Titan. Until you remember that Keiko is a Japanese woman living in 1954, which means that she lived through her country being devastated by the use of atomic weapons, which occurred less than a decade prior. She likely sees him as an innocent animal who's being specifically targeted with a nuclear weapon.
Cate's reaction when finding out her father was cheating on her mother is far more hostile and bitter compared to Kentaro who is in the exact same situation but he at least rationalizes that yes their father screwed them over but isn't completely irredeemable. It's later revealed that prior to G-Day, Cate was cheating on her girlfriend and sleeping with another woman, well before she found out her father had a Secret Other Family. She is projecting her own self-loathing and guilt onto her father.
So far in this series, all the Titans seen have displayed some form of aggression towards humans - the Endoswarmers's first instinct is to hunt and eat Keiko and Lee, Frost Vark goes after any heat source, even the Ion Dragon initially chases Keiko, Bill, and Lee seeing them as invaders in its territory. But Godzilla in all his scenes is the only one who made no attempt to deliberately attack or hurt humans, any injuries or incidents with humans were done entirely by accident, and in episode 6, he just walks away after the main characters disturb his sleeping spot. It helps both Keiko and decades later, her granddaughter Cate, realize that Godzilla is more than just a monster to be killed or feared but that he is an intelligent being not unlike themselves.
Keiko estimates that she spent nearly two months down by herself in Hollow Earth/Axis Mundi, while Lee Shaw spent about a week there when he first visited it, and his second trip with May and Cate lasted less than a day. Respectively, on the surface world, roughly 56 years had passed for Keiko, while Lee was gone for 20 years, and Lee, May, and Cate were gone for two years, and in all cases it barely seemed as if they aged a day when they returned (far moreso in Keiko's and Lee's cases). Time passing much, much slower in Hollow Earth/Axis Mundi certainly explains why Godzilla at least is as old as he is, since if he's stayed there for any extended length of time, such as a few years, it would have resulted in centuries and possibly entire millennia passing by on the surface.
It is fitting that in "Episode 10: Beyond Logic" it is revealed that Cate, May and Keiko have arrived in the year 2017 and landed in Skull Island of all places. After all that was the year audiences were introduced to both this version the island and its most famous inhabitant.
In Godzilla: King of the Monsters, an Easter Egg in the Creative Closing Credits features a conspiracy theorist accusing Monarch of building a "mechanized giant" on Skull Island. Whilst Mechagodzilla does appear in the following movie, Godzilla vs. Kong, it's being developed in Pensacola and Hong Kong instead, and it has absolutely no connection to Skull Island except for Skullcrawlers that Apex are attaining as eggs being used as cannon fodder in the Mecha's test runs. The revelation in "Beyond Logic" that Apex Cybernetics, the corporation who will build Mechagodzilla, have a fully-functional research station on Skull Island in the late 2010s provides a possible bridge between the two. It also provides a possible explanation for where and how Apex attained their Skullcrawler cannon fodder.
Godzilla being the one to show up and exiting the Hollow Earth Tunnel to help Lee, Cate, Keiko and May seems strangely convenient until you remember in the past, Godzilla had heard a prototype of the gamma stimulator before and recently again when Hiroshi was trying to locate a Titan where Godzilla was sleeping. Godzilla may have been curious enough to check it out since Keiko had been sending out the signal for some time, perhaps making a connection that humans were involved, especially given that Godzilla's gaze initially zooms in on the group and he appeared a bit annoyed.
Tying into this, it's fitting that it's Godzilla and the Ion Dragon that the group sees together in the last episode. The Ion Dragon was the first Titan that Keiko, Lee and Bill interacted with, thus the reason why Monarch started. Godzilla was the Titan that helped Monarch prove the existence of Titans to the government, keeping Monarch alive.
Why did a pissed Kong turn up during the final scene just in time to show the viewer where the main cast now are, within minutes of the Axis Mundi group's emergence and the ensuing drama? Kong most likely sensed the Axis Mundi rift when it spat the group's pod up, and he's come to investigate.
The series completely recontextualizes Bill Randa's personality in Kong: Skull Island into a more tragic character. Like Keiko, he was awed at the sight of Titans when they emerge, and was willing to defend Keiko from racist comments, regardless if they're military. Then he finds out Keiko is a single widowed mother trying to raise Hiroshi, and offers to help them. After marrying her and becoming Hiroshi's stepfather, he loses Keiko in the Kazakhstan nuclear power plant, then loses his best friend when the latter is presumed killed in the Hollow Earth for 20 years, which explains Bill's personality in Kong: Skull Island. Due to his unfortunate death, Bill wouldn't live long enough to see that his best friend and wife were both alive, nor to see his stepson joining Monarch.
"Beyond Logic" adds even more of this to May's home life. She's away from her family for over two years thanks to her actions with AET, unable to come home and only making the most sporadic of contact with her sister. She's cleared, has a joyful reunion with her family, then leaves to help the Randas as they helped her - and is trapped in Axis Mundi for another two years in our time. Her family again have no idea what's going on or what's happened to her, and this time, there's no fleeting phone calls to confirm she's still alive.
