First I'd like to say that if I hadn't heard of this questionnaire, I might never have bothered with KS. Deservedly or not, KS is known for being "that visual novel made by 4chan where you hit on crippled chicks".
A few times during my career in game development I've had testers come to me to discuss how certain sequences I presented affected them, and helped them reflect on their own lives (sadly, these games never made it to market - long story - details under NDA). I always took time out for this, and not so much as a professional because there wasn't enough hours in the day to take notes and analyze my observations. All I could really do was give them the simple human courtesy of letting them talk out something that had an effect on them. I've often felt that not recording those chats was a missed opportunity.
Frankly if research into Katawa Shoujo can shine a light on the hows and whys (or at least give us better questions), I think we'll all be the richer for having that knowledge. I'm glad to do my part.
FULL DISCLOSURE: I skipped a LOT of content. I mean easily half of it. I generally only gave the 3rd and 4th acts a very thorough reading, and not always even then. It may sound strange, but I feel like I probably got the best possible experience for having done it this way. If it means I misunderstand some aspects of the plot or the characters, so be it. I firmly believe KS might have been twice as good if it were half as long. Everything I say should be qualified with "from what I've read"
1. Which girl's thread affected you the most emotionally? Why did it do this?
Emi got the most consistent strong reactions, but when Shizune's arc hit me, it hit the hardest (discussed in Question 6).
As for Emi, everything about her cuts through my defenses: her design, her expressions, her infectious energy, and what she goes through during her arc. The "Emis" I've met in real life have always left me twitterpated. This is much to the bemusement of my more Hanako-like life partner who finds them offensively chipper. She often chides me for liking those spirited "girly girls". We both take it in good humor.
I won't discuss Emi in question 6 is because I don't think there's much to say. To understand why I react to Emi, you would need to understand things about me that I don't necessarily understand myself, let alone have a coherent explanation for. There were no standout "look at this" moments I could point to, just broad trends that appealed to my sensibilities in real but indistinct ways.
2. Which girl's thread did you successfully complete first (good ending)? How did you reach the good end of this thread? Did you use a guide, or did you answer the questions according to your own thoughts, as I did?
Hanako. I did what I'd really have done. I didn't want to freak her out by being too forward, but I did also want her to be used to me since we needed to share a common space.
Then it turns into this whole big deal. O_o
Dude just wanted to share the library with her.
I didn't use a guide until relatively late (3rd or 4th run) and by then many options were checked off anyway.
3. In what order would you rate the quality of the girls' threads?
Eeek! They're all so different that ranking them is difficult. I felt they all needed to be trimmed down, Shizune's and Lilly's most notably.
Emi - Emi felt the most relatable, and is probably the one I'm going to think of if someone casually mentions KS. I think I read her arc more thoroughly than the others, but that says more about me than it does about the quality of Emi's arc.
Shizune - Hit me like a ton of bricks. She could have taken the top spot with a little trimming. I skipped way too much for how interested I was in the material. This was a difficult one to place in light of my answer to Question 6 (do I forgive some non-trivial flaws in favor of something I thought was very clever? I guess I did...), and I can see why this arc takes so many bottom spots.
Hanako - I feel bad for putting Hanako "somewhere in the middle" given my own relationship. I can tell you from experience this was perhaps the most hopelessly idealized arc. The other characters seemed to have some basis in reality. Helping the shy girl come out of her shell is a common male fantasy, and unlike some of the other arcs this one really fails to capture how agonizing this can be. For a work that was generally well informed, and well thought out, this was a bit of a let down.
Lilly - I probably skipped as much content as Shizune, and without seeing anything that really blasted me. Best illustrations in the game though. Given how many top spots this one has taken, I may give this arc a second shot. One of my problems with it is that Hanako was more interesting in this arc than Lily.
Rin - Rin had the narrowest focus, with much less of the "A-plot/B-Plot" formula that characterized the other arcs. This was a problem for me because I didn't connect with the theme of 'understanding'. With nothing else to grab on to, I joylessly pushed through this arc until the very end, where it picked up immensely.
Kenji - I skipped about 80% of Kenji's material. I'd slow down sometimes and check the text history to see if I wanted to read this. Not really.
4. If there was a single word which describes the key a player must remember to complete each girl's thread, what would that word be for each girl?
Emi - Indirect
Shizune -
Refuse 
Hanako - Discretion
Lilly- Confront
Rin- Support
5. How much time did it take you to complete each girl's thread? (Play time, not total IRL time)
About 2 hours per character give or take 30 minutes. Hard to say because I'd do a few scenes, then go back to work, then do a few more scenes. This is all while leaving the game running. So my play time measured in-game is not representative.
6. Give an example of a particularly effective piece of writing from your favorite girl's thread.
I hate to be that guy, but what IS writing to you? This term is often conflated with simple technical wordsmithing/composition (which itself comprises grammar, and the use of language in a general sense), as well as matters of characterization, pacing, and overall approach to themes and tone.
If you're talking about simply the written passages as they are written, well... I can answer both questions 6 and 7 here: none of them stand out to me. Almost nothing in KS stayed in my head like the famous opening to Fear and Loathing in Las Vegas that I can quote verbatim (huge bats!). I found Katawa Shoujo made up of an unmemorable collection of words.
But that's where KS is more than the sum of its (parts... no...) execution. There are aspects of KS that were clearly well thought out: the significance of a girl sensitive about her appearance being best friends with a girl that can't see was never lost on me (this is just one obvious example). To the writers' credit, these matters are seldom addressed directly (unless it happens in one of the many large sections I skipped. In which case I like my version better!)
The most impactful scene for me wasn't even in my favorite girl's thread. It was Shizune's
binding of Hisao. The act of binding someone who can only speak to you in sign gave me a very strong reaction. This is "shut up and kiss me" turned up to 11. This is, "I am taking your voice." Her intentions seemed innocent enough. To her this probably felt like putting on the training wheels. Now everything is nice and safe, and she can explore at her own pace. It's almost sweet, for a rape scene. I found this one of the most disturbing scenes in KS because it highlights how dangerously selfish Shizune can be.
Various scenes might have made a tug for my heart strings (or other anatomy) with greater or lesser effectiveness, but I often found myself shrugging and saying "That's life" (another reason I relate to Emi's arc in a broad, but less particular sense). The above sequence was something altogether different - it transformed the entire arc for me, sending a shockwave in all directions through the narrative.
7. Give an example of a particularly effective piece of writing from your least favorite girl's thread.
I won't lie; I nearly gave up on Rin's arc. I followed through only for the sake of this questionnaire. I kept thinking "I get you Rin, it's not what it looks like". I guess that's why I didn't click with the bulk Rin's arc: we're too alike. I speak 'artist'.
Then somewhere near the end, she has a conversation with Hisao that mirrors ones I've had many times, with me on Rin's end. The KS writing team clearly grasps how this aspect of the creative process can make some people behave strangely. Another example of the thought behind KS shining through an otherwise forgettable technical presentation (and why your questions about "writing" "quality" are difficult for me to answer as directly as some other responders).
Yes, being an artist is exactly like eating a watermelon Popsicle. Bravo! One of the few bits of wordsmithing that even kinda sorta stuck.
And not long after this, Nomiya has a talk with Rin, and it's one I've had many times with me on Nomiya's end.
It's a shame those parts came so late.
8. Do you feel that, after playing Katawa Shoujo, that you are better equipped emotionally for a real-life relationship? Why or why not? If you are currently in a relationship, do you feel that playing KS will allow you to strengthen it? Why or why not?
*chuckles* Oh my no. It's a fantasy game - just an extremely endearing one. That doesn't mean someone couldn't pick up something. I think Hisao is a good role model in some ways. He's caring without being a doormat, and shows some real assertiveness when standing his ground. I especially appreciate how his sexual exploits are byproducts of genuine affection rather than the objective from the beginning.
I am in a relationship, but I don't think KS made any lasting impressions on it. I asked my partner about this and she said there's nothing something like KS could really do in our case. We're two people with solid, time tested strategies for living together and dealing with our differences, and we
like each other. KS can't touch that, although I think it did portray it.
PS
INFP representin'
PPS I'm aware of the irony of saying "KS would better if it was half as long" and making a post for which the same is true. This IS the trimmed version.
