Hello! Since you seem to be getting a lot of character comparison asks, I figured I’d ask if you have any thoughts on the similarities and differences between Ken and Koichi, and also their relationship with darkness? At first glance they seem very similar but I feel the way they view darkness- and perhaps the darker parts of themselves- differs quite a bit.
The two of them definitely have similar base profiles at first, but start to really veer off in different directions after that!
I think the one thing that's most different between the two is that, quite simply, their "base personalities" -- that is, how they act in normal situations separated from all the stuff going on with Digimon fighting -- are actually fairly different to begin with. One thing that might surprise people is that Kouichi actually uses the more assertive/aggressive pronoun ore, contrary to what his supposedly “shy” personality might suggest (of the Frontier boys, only Tomoki uses the more polite boku, and I think it’s in line with Frontier generally portraying its kids as less naturally well-behaved and a bit more misfit). Kouichi’s “shyness” in Frontier is really implied to just be out of the circumstances of him being a bit awkward around the kids he’d been fighting for a period, and especially not sure how to approach Kouji, but Things I Want to Tell You implies that he’d actually had a full-on social friend circle (mentioning friends at school and playing soccer). The only part that made him “out of place” like the other Frontier kids was really the part right before the series, when he learned he’d had a brother, had to question what that implied, started fostering feelings of jealousy towards him, and ended up “passed over” for being chosen instead of how Kouji was, but for the most part his personality doesn’t seem to be that fundamentally different from Kouji’s (there's a point made in a scene in Frontier episode 40 where the twins are looking at Takuya with nearly the exact same expression).
Ken, on the other hand, does use the polite pronoun boku, and although he’s still a fairly casual person (his speech pattern is slightly more casual than Takeru’s), he is kind of...a polite nerd, for lack of a better way to put it. That penchant for intellectuality wasn’t entirely the Dark Seed’s doing -- he’s gone on infamous “trivial fact” spiels like about the origin of Christmas or Japanese hot springs. In contrast to the more easygoing Daisuke, he takes things really seriously, and one could describe him as “so overly serious about things he sometimes rolls into stupid”. He’s also rather tidy (he puts his chopsticks neatly on the bowl when eating, his Digital World outfit is his school uniform, he’s constantly tucking in both his summer and winter blouses, and even his Kizuna outfits are slightly formal), and because he does seem to carry himself softly, he has a stronger image of being a “nice and polite person” who doesn’t act roughly by default. Less so because he can’t be rough or aggressive, but more because he doesn’t want to be -- you can think of him as basically holding back his cards until the time is right or stronger force is called for (meaning he can seem mild-mannered, until he suddenly drops some sassy zingers right when you least expect it).
There are some similarities that go beyond their base profiles; it’s interesting how “jealousy” seems to be part of both of their initial motivations (and, in an interesting meta twist, one of the original ideas for Ken and Osamu was for them to be twins). However, as you said, they have a somewhat differing attitude in terms of what “darkness” is, and a lot of it has to do with a combination of what that even means in Adventure/02′s narrative versus Frontier’s, and what that meant to each of them personally. Ken had an outright self-inflicted identity crisis and an awareness that his fall came from his own personal vices, and the issue is casted in Adventure/02 as a problem of “balance”; Ken himself understands in 02 episode 23 that he has to accept everything in himself, and Takeru reminds him in 02 episode 37 that you can’t eradicate it entirely, but Ken of course retains an aversion to contexts where they’re obviously too much in excess. Kouichi, on the other hand, was probably not going to have a complete emotional meltdown to that degree had it not been for Cherubimon’s interference (although he still wasn’t necessarily having a great time), so being free from that influence means that, with his head cleared, he’s able to confidently deny going back there again and have faith in his ability to use it for good, especially because the part keeping it balanced -- his brother Kouji, as the light -- is able to be there and fight alongside him. His problem was addressed by learning to work alongside and get to know said brother, instead of living in jealousy of him.
It’s also interesting to see how their future plans end up going, since we now have “distant future” canon material for both 02 and Frontier; Ken had “expectations” put on him to the point it practically ripped him apart and gave him an outright identity crisis, so his future involves him allowing himself to not have to live to expectations nearly as much; by the time of Kizuna, he’s still dabbling in soccer and various hobbies and being chaotic with his friends, his “psychology” degree is not even mentioned anywhere except in his official profiles because of how much it’s a comparative non-issue in his life at the moment, and while he’s certainly still selfless, he’s still at the point where being able to just enjoy life as it is at all is a big deal. Even if he hasn’t found a goal in life to completely commit to yet, at the very least, he has the other members of the 02 group to support him, and it’s still important that he’s dedicating his efforts to supporting them in turn. Kouichi, on the other hand, didn’t have to worry about that kind of identity crisis, but he did have to worry about seeing his mother’s selfless streak meaning she was constantly ruining her health for others -- so, having taken on some of that selflessness, he’s decided to single-mindedly pursue a dream of going to medical school to help his mother. Keep in mind that he arguably has an even higher hurdle than our other single-minded prospective doctor, Kido Jou, because unlike the Kido family’s existing esteemed line, Kouichi’s not-exactly-well-to-do background means he’d had to scrounge up funds by being a paper boy while he was at it -- so that’s a pretty big uphill battle he’s taking, but he’s doing it because he knows that’s what he wants, and he also has his brother properly keeping up with him, and in touch with both him and his family situation.
