Well, aside from Snupin, the other obvious parallel couple for Iwaki/Katou is Ryo/Dee from the FAKE manga, which has an eager Dee unabashedly pursuing a reluctant Ryo, much as Katou pursues a reluctant Iwaki. It's been awhile since I've read the manga, but I seem to have the impression that Ryo initially protested that he wasn't gay, much as Iwaki did. There's also the fact that both Katou and Dee are the more exuberant, outgoing types compared to the more reserved Iwaki and Ryo. Iwaki and Ryo are also the more responsible ones in the pairing, and are always scolding Katou and Dee for being immature.

Theoretically, both couples are in professions where their careers could be in jeopardy if they were outed as gay. "Theoretically" because although a gay cop would normally have a hard time with his macho colleagues, the police station where Ryo and Dee work is practically a gay love-fest, with one coworker pursuing Ryo, and another pursuing Dee! ^_^

Iwaki and Katou's relationship does cause some trouble for them, mainly mass media scandals, but as Kikuchi points out, it also made them popular with the public. Er...so I'm not sure what my point is. Just that their relationships ought to cause problems with their careers, but for the most part they rise above it, I guess.

I don't exactly have another parallel couple in mind, but red_day_dawning was saying that I wrote Kikuchi as a Slytherin in my "Comeback" fic. I sort of hinted at a possible future Kikuchi/Onozuka romance in that fic, and I realized that I liked both characters so much (both together and apart) because they're Slytherin types. (Actually, I've been thinking of writing a "Which Hogwarts House would the Harudaki characters be Sorted into?" post. ^_^)

Mmm, I think my own non-canon pairing Shu/Shouji is sort of Severus/Lucius-y, just age-reversed. The rich, cool, manipulative guy and the working-class, sort of, snarky person.

As for Iwaki and Katou, I just liked them, unrelated to the Snupin connection, but the similarities were quite clear right away. Didn't precisely made it worse.

I think it is the contrast between the open, happy type of person and the snarky, introvert that does it because it both creates conflicts and make them able to support each other.

Personally -as the Snape/Iwaki-like type- I'd go insane living with someone like Remus or Katou. Then again I knew that already, so I am not sure that insight came from reading Snupin.