I've had a realization about Spirit Evolution, in terms of what is it. Basically, it's an overlay. According to the definition of overlay that I found regarding data, it is one of two or more pieces of data that can be loaded to a predetermined memory region on demand. Additionally: it can be stored like any other piece of data, it can be changed with another overlay at any time and only one overlay can occupy that space at a time. Sounds familiar, right?
On that note, the dub does something brilliant in adding, "Execute," before the Digidestined cry our "Spirit Evolution" to fit the lip flaps of what was originally, "Spi-ri-to." On a computer, you "execute" a program. What is a Digivolution if not a computer program?
When Takuya and Koji gained the ability for Unity Spirit Evolution, it always bugged me that the Ice Spirit was a key part for the Fire Spirit. However it just hit me not that long ago; the Ice Spirit for the Fire Spirit and the Darkness Spirit for the Light Spirit were for control. All the other spirits were used to up the power of the Light and Fire Spirits, but they needed a counter productive spirit in order to have that power be controllable.
If I had to guess I'd say it's most likely because Takuya and Koji had stronger or more aggressive personalities than Tommy and Koichi. It also might be because they were the ones who initiated the evolution.
It even goes further than that, Takuya has the spirit of Earth already in his digivice, and Koji has the spirit of water. These two spirits also act as control. So, two for empowerment (Wind and Wood for Fire and Lightning and Metal for Light) and two for control (Ice and Earth for Fire and Water and Darkness for Light).
Having the humans become Digimon themselves may be an odd plot element, but it actually makes perfect sense! Look to Windward... I mean the previous seasons for comfirmation.
Season 1: The movie concluding the season ends with two Digimon physically merging together to deliver a thorough asskicking.
Season 3: A slightly different variation of Fusion Dance, between a physical human and a physical Digimon becomes the gimmick for that season.
Come Season 4, we have humans physically merging together with the souls of various Digimon to fight as one.
Some could see it a different way, considering things went from the kids each depending on their own Digimon to do all the fighting while they retreated to safety in season 1 to sharing Digimon at a 2 to 1 ratio in season 2 to merging with their Digimon in season 3 to becoming Digimon themselves in season 4
Due to Japanese Ranguage, the "Ko" in Koichi's name can be translated as "Go", making his name "Goichi" and giving his name a double meaning, as while Koichi is the first-born twin, Koji's elder twin, he is also the embodiment of five plus one.
Why is Mecurymon/Sakkakumon a schemer who takes pride of his mental tricks and gambits? His power is inherited from AncientWisemon, who is based on Zhuge Liang, or Komei, the legendary strategist of Shu Han.
Lucemon actually thought he was God. In The Bible, God is described both as a being of blindinglight and deepshadow. Lucemon Falldown mode had both of these attributes, except he was evil and crazy. He convinced himself that he was God and thus only he should rule over everything.
Although much maligned, the Royal Knights arc actually shows what is probably the most realistic portrayal of Digimon gaining experience and strength in the entire series. They go from being new to the form and getting curb-stomped, to giving the knights some trouble, to fighting them on even footing, to finally beating them.
How was Takuya able to predict what that storm would do after he returned to the Digital World? It makes some sense when you consider that the Warriors' combined form is Susanoomon. Susanoo is the god of storms in Japanese Mythology.
Why are the Human-spirit Digimon Adult-classed? Because, it a way, they evolved from the chosen children.
At first, Koji being the Warrior of Light appears to be just a Power Stereotype Flip, with his stoic, "lone wolf" persona being a far cry from the pure-hearted, innocent characters that tend to be associated with the element of light; it is, in particular, a far cry from Kari, the other notable main character associated with light in the Digimon anime series. Then we find out who Duskmon really is...
In Digimon V-Tamer 01, Hideto Fujimoto says it is impossible for ancient type Digimon to reach level six(JP Ultimate, EN Mega), yet here are a ten strong group of level six ancients? Why were level six ancients thought to be impossible? Because Digimon express themselves by overwriting their own data. Ancient types had violent overwrites that made them powerful at the cost of drastically shortening their lifespans. Even though the warrior ten won the game of life and got that far, chances are they weren't long for the world. So they opted to stick around in spirit, so their levels can be attained more easily. It also explains the preference of human hosts. Humans don't overwrite data, so their lifespans are unaffected. However, the bestial aspect of an ancient Digimon spirit will still overwhelm a human mind...unless that human is focused on preserving its group, since humans are social beasts.
What happens if the kids' data were scanned? Would they turn into a digi-egg? Would they DIE, for real? There's no indication that there are digi eggs for data that AREN'T digimon...
My own personal theory on this is another type of horror - they get turned into Digitama and hatch as Digimon, permanently stuck in their Digimon forms. Mainly because if we see the Digital World as a giant computer running on computer rules, it might just format the 'strange data' into something it can process.
What happened to all the digi-eggs after the moons were blown up? Can eggs be perma-destroyed?
Doubtfully, considering how the series goes out of its way to avert the above trope (pretty much every time a Digimon is scanned, a Digitama is shown to fly away).
So... what happened to the other Trailmon and human kids in the first episode? We know some of them wound up in the Digital World... but there were more Trailmon and a lot more kids...
They were sent back home by Ophanemon. The ones with Angemon were the ones that refused to go.
There's a layer of horror revealed after Kouji takes a sword for Takuya. In a later episode, his balance (normally excellent) is off, his breathing is off-kilter and he's clearly holding his ribs, meaning that despite his Digimon form taking most of the damage, he still took a great deal of damage to his human body. This means any time the kids are hit with enough force, they're not only in danger because they're reduced to normal humans but because there might be damage that could prevent them from running away or dodging.
If the God that Lucemon was trying to overthrow was King Drasil, he was really doing a great job at it based on the duo of Knights that he was subverting; Dynasmon and Lordknightmon. These two alongside Duftmon are the most devoted to King Drasil and they basically do anything that they were told, namely wiping out all of humanity. Even when every other knight (including Craniamon) starts questioning Drasil for his actions, Dynasmon and Lordknightmon do not. The very fact that Lucemon was able of subverting Drasil's two most unerringly loyal enforcers meant that if the Legendary Warriors didn't stop him he might very likely have the power to go directly for Drasil's head.