To celebrate the 10-year anniversary of Gundam Wing on Toonami/Midnight Run, here's an interview with the creators of Gundam Wing, taken in around 2005 (for its 10 year anniversary in Japan).
Quote: Interviewees: Producer Hideyuki Tomioka from Sunrise, Head Writer Katsuyuki Sumizawa
Setting: The group of five concept was decided primarily because of G. Shenlong and Heavyarms were the first designs cemented, and Wing wasn't made the leader until late in the process. At one point they considered the name "Meteor Gundam" in reference to Operation Meteor. It was Bandai that suggested "A Gundam that transforms and flies through the skies". Apparently the writers sat down and, in one week, belted out the concepts for the main cast, MS, and the first 40 episodes, causing Director Masashi Ikeda to comment "It's like you're doing First, Zeta, and G all at once!"
Characters: Ikeda had a hand in the characters' designs, since he can draw. Basically, he made rough sketches of how he pictured the characters, then handed them off to Character Designer Shuko Murase to finish. Murase was specifically chosen by Ikeda because they worked together on Samurai Troopers (Ronin Warriors) and Ikeda wanted designs that would appeal to female fans. In the early phases, the characters' iconic costumes were set, such as Heero's tank top and shorts. Heero was modeled on Japanese actress Yuki Uchida. At one point Wu Fei was going to be African and a Newtype with the power to tell whether people were good or evil, but he was changed to Chinese in light of G's Sai Saici. The keywords for Duo and Quatre's designs were "Shinigami" and "Arab King", respectively. Trowa's name is derived from Tim Burton, because Ikeda is a fan of his work and directorial style.
Heero: The interviewer comments that at the time, Heero was quite unique as a "cool genius protagonist", an archetype that's become more common since. They comment that it seemed unusual simply because most Gundam protagonists are the immature type who grow over time, and say that Duo more closely matches the "traditional" Gundam hero mold. Initially it looked like Heero would be the "supporting actor", but he was made the star, and Duo subsequently became extremely popular. They muse that normally a supporting character with cruel eyes isn't too popular, but as the protagonist it ended up working out in Heero's favor. They consider it Ikeda's mark to be able to handle five well-done protagonists, but comment that Quatre wasn't too popular, with female viewers calling him "Space Heart Jerk" (Uchuu no Kokoro Yarou). Consequently, Sandrock models didn't sell too well. At the time Ikeda said "Sandrock's shotels are useless if they don't cut things in a cross!"
OZ Characters: Originally Une was going to be a clumsy country girl who was nice to Treize. The idea was cut, but elements remained, such as Treize encouraging her to act a bit more elegantly (seen in episode 10, conveyed to Une by Noin), which was brought up again in the scene where Treize is bathing (Sumizawa admits he isn't sure why they chose to do the scene in the bath). Ikeda commented that the idea of a jacuzzi was funny, and suggested the rose essence, which meant Une had to be there. After that, there were bigger changes. Noin was originally going to be a man and play a Garma role to Zechs' Char, but they decided to make her female and a love interest.
Zechs and Noin: The bit where they get together again and Noin taps their swords was done by Ikeda, and Sumizawa comments that in retrospect it was kind of cool. They made jokes when Ikeda pitched the scene, but admit that the filmed version ended up being cool.
Lines and Scenes: At the stage where Sumizawa was writing the series bible, he was already working out lines (catchphrases?) for the cast. Sumizawa comments that a really good line can portray a character's personality extremely well. However, not all the lines he put into the bible were written in at first, they ended up being used later in the series. He comments that hearing Midorikawa deliver Heero's "Life comes cheap, especially mine" line in a game recently after so long impressed him, and he comments about them redoing the lines for games every so often. He discusses Treize and Wu Fei's exchange in episode 48 ("Just how many people have died for you?!" "As of yesterday, ninety-eight thousand, eight hundred and twenty-two."), commenting that a regular character would have responded "That's no concern of mine" and says that Treize's response shows how cool he is.
Tomioka (after teasing Sumizawa for remembering that stuff twelve years after the series), mentions lines from the first coul that seemed funny but had real impact, like Relena's "Heero, come back and kill me!" or Heero's "Mission accepted". Sumizawa comments that normally killing the protagonist in the 10th episode is impossible, but when he pitched the idea, Ikeda's response was "Interesting!" so they ran with it. Even though they had started on 11's script, Ikeda said "Self-destructing...interesting. Do it!" When Sumizawa wrote it, he thought to himself "Heero's dead for real this time, isn't he?" and wasn't convinced by the animation - it actually worried him.Composition: Sumizawa comments that when it comes to series composition, one big difference is that writers hand off duties like a relay, as opposed to a novel where one person writes the whole thing. Because there were five mains, things were done differently, but the setting allowed the writing for the boys to flow rather easily. The differences and similarities between the boys changed the dialog; Heero talking to Duo or Quatre would be vastly different from him talking to Trowa. As they fought individually things got worse until they finally united. Because they were five complete people, when put together, they'd act selfishly, but the self-destruct changed that. Katsuhiko Chiba wrote that scene all himself, and in retrospect it isn't surprising. A regular producer would have said "Hold on, let's reconsider", but Tomioka gave it the go-ahead. He says that he thought the self-destruct was an interesting concept, and Sumizawa says that getting a producer to say things like that is a victory.
Casting: Tomioka and Ikeda handled the voice casting. Tomioka says that because the atmosphere was so different and conflicting with "normal" Gundam, it took extra work to achieve a satisfactory result. He mentions that Gundam seems to hit its big moments every ten years or so, saying that Zeta came almost ten years after First, and Wing ten years after that. His attitude was validated ten years after Wing when Seed came around. When the first episode was shown to Sunrise, they weren't surprised by the action in the first half, but were thrown off by the calmer school aspects in the second. When Wing sank, they probably thought things like "You can't sell toys of something at the bottom of the sea!" and "How's he going to use it?" They were convinced that it was good work, and didn't mind the OP, which Sumizawa thought they would. Tomioka thought the OP would be worse received, because it didn't feel like the intro to that kind of show. They had to tell singer Minami Takayama to "make it feel more like an intro", and afterwards Ikeda and a couple of others said "I guess we can make it work as an OP."
Endless Waltz: The show was popular and they were asked to do a continuation, but neither Tomioka nor Ikeda intended to make one following the TV series' end. Sumizawa was the opposite, feeling bothered a month after the finale. He felt like it cut off rather abruptly. At that time, Tomioka came to ask if he'd write a continuation, and he enthusiastically agreed.
The format was decided as three episodes, and they intended to give Wing a definite ending. Fortunately, the show's popularity hung on following the series thanks to games and manga, so the production didn't feel pointless; they were also getting requests to do a sequel. Tomioka said that they should sit down and write the ending definitively - except that the title was "Endless Waltz", sounding almost like a satire of their goal.
The idea to throw the Gundams into the sun was devised by Ikeda at the end of the series; there was no more war, so there was no more need for the Gundams. That was the point where they started the story. They muse that Wing had low mechanical focus, replacing MS details with drama, which probably accounts for the show's higher popularity with girls than boys. EW had well-done mecha scenes, which probably made it sell better to boys.
Katoki was the one who wanted to give Wing literal wings; the animators weren't happy with the tougher design. Sumizawa comments that the animators had Disney's animation staff come in and observed them to get an idea of how to handle the wings. The response was apparently "The Japanese draw feathers that dance and swirl by hand! Crazy!" They remark that the digital remaster restores part of the image cut off originally, and say that a digital TV seems to clear up all the problems.