About "light" and "darkness" in Digimon
If you are a member of Digimon fandom long enough, you will know a fact: there're lots of fic crossover between 02 and Frontier.
This is not weird or surprising. First, 02 and Frontier are both in the Seki quartet, the first four seasons of Digimon franchise. And going against common negative opinions of a part of fandom about these two seasons, 02 and Frontier do get quite a good love from many fans. They also do have many uncovered, contradicting, or just curious-inspired parts, so fanfics are just being numerous!
And interestingly: 02 and Frontier both get quite same treating from fandom because they are somewhat similar outsidely. The characters are "flat" and " bad stereotype". the plot is "messed up", and the two seasons "don't have deep messages". Of course, these are false ideas, but 02 and Frontier have a specific between-line writing that is difficult to understand and sympathize. I really don't blame the fans to misread!
02 and Frontier has characters both known for particularly tight group dynamics compared to others, and both groups are known to be somewhat "chaotic" (and, affectionately, “very stupid”). With 02, that is from lack of planning or being too airheaded. The Frontier gangs, on the other hand, can and will cause trouble and will be very proud of it. And somehow escape it perfectly, of course.
So? Basically, "Takeru would hate Kouichi because of him being the Warrior of Darkness. 02 group would be wary about Kouichi (and Frontier gangs because of that as well (especially Hikari too)." is a (in)famous trope in crossover between 02 and Frontier. Let's debunk it.
First, this is out of character of Takeru. People tends to forget that Takeru is a polite, respectful and carefree person. If someone tells him "Hey, there's a Warrior of Darkness!", well... He won't react so boldful. He is actually very infamous for keeping his emotions inside, so unless he saw something really pissed him off, I don't think he will act too angrious. Takeru never blew up at anyone without some kind of good reason; it’s just that the level of his intensity was unnerving.
Takeru will pretend he has it together and has everything under control. He won't show any of his negative feeling, instead, he would investigate and find out the truth himself... while dodging questions and his own emotions. He simply handles everything with a “yeah, okay, sure! :)” attitude. Except when really needed, Takeru... rarely do things that are easily to do to solve problem, but passively deal with them when they run to his face. So if he completely snapped at Kouichi for no reason besides him being darkness-associated, that’d be really out of character.
And beside, Takeru is a quite social and generally nice individual, who treat other kindly! I don't really get how others can misread his personality in another way. Let's move to the next point.
Second, Takeru doesn't hate darkness, or have a black-and-white-morality. The thing is that Takeru himself says that he's not going to inherently hate anything darkness-related on sight (in 02 episode 34):
Takeru is pretty clear about what exactly he hates earlier in that episode:
Trying to change the world with that power...Trying to conquer the world...It's unforgivable!
Basically, he hates people who try to toy with darkness to play God, “create sad lives” like BlackWarGreymon with it, and do things that resemble Devimon in Adventure (like “dabbling” in the powers of darkness much like the Kaiser would later).
But in regards to darkness itself, you can find a proof three episodes later that Takeru is pretty understanding of the topic (02 episode 37):
...so he’d probably treat the twins with a lot of respect.
So while Takeru would probably hate Duskmon if he didn’t know more about what was going on behind him, that's obvious, if he actually learns about Kouichi’s situation and background, not only would he be very likely to sympathize with Kouichi and advocate on his behalf, he’d also probably fly into a murderous rage at Cherubimon for exploiting the powers of darkness to make Kouichi suffer! And because that kind of topic really pisses him off, he might even get more pissed off than Kouichi himself is about it.
Actually, these kinds of tropes just throw all character development of Takeru and turn him into a flat character. Takeru also would become a writer, and you can't think that he just skipped all nice characters with darkness-themes.
And mentioned that, Ken and Kouichi are usually being simplified to be just as the same as each other. Although they have many similar features, like "thoughtful, perceptive, very in touch with feelings, VERY assertive, resilient, strong in heart, and kind out of choice even when doesn’t have to be", but they are different individuals. In a language level, Kouichi uses the "ore" assertive pronoun while Ken uses the "boku" more gentle one.
In conclusion! Takeru would be the one to clarify with the Frontier gangs to make sure that Kouichi isn't dabbling in the powers of darkness for the others' sake. And then he'd become the most vicious protector of the twins. And the rest of the Adventurers would just follow his lead since Takeru and Hikari with their sensitivity to the balance of the world.
