I found an interview with KEI somewhere about the design of Hatsune Miku, Kagamine Rin/Len, and Megurine Luka somewhere! Will post for you guys!
NOTE: I did not make the interview, nor did I post it on the internet. I'm just sharing with you guys.
Q: How did you come up with Miku's look? Was it your own decision or was it based on specifications from here makers?
There were no requests reguarding her hair or clothing. All I recieved was "she's an android" along with some specs for her color design and certain auxillary parts. Miku was given a particular YAMAHA synthesizer's signature blue-green color and some of the same synthesizer motifs on her clothing. For example ~ the print on her skirt is actually based on a panel from the real synthesizer.
Q: It seems cosplayers who want to dress up as Hatsune Miku could learn a lot by checking out some synthesizers. Was it your idea to incorporate things like that?
No, I know next to nothing about synthesizers. So I had to have the makers point me in the right direction and correct my initial sketches. For example: after I showed them my roughs for Kagamine Len, they suggested he have and M-D cable (a part used to connect instruments and equipment)... so I added one to his right leg.
Q: Come to think of it, the Kagamine twins' leg covers have really specialized designs too. Are those based on music equipment as well?
The two of them are also based on a YAMAHA synthesizer. Even their theme color comes from a synthesizer. That's why the details on their leg covers aren't the same for both legs. The synthesizer's they're based on have speakers on only one side. Rin's details are on her left leg and Len's are on his right. I lined them up in designs to that Rin would show her left leg and Len, his right.
Q: I see. It's a natural idea for twin characters, huh?
I didn't actually intend for them to be twins. I was told that they're more like mirrors. It's just that when I designed them, I did it at exactly the same time. No sooner was Rin finished than I'd started drawing roughs of Len.
Q: Was there anything else you were requested to incorporate into the VOCALOIDs' designs?
Well, I was given their approximate ages. But I got them along with the information that they were also androids. I'm not sure if androids even age, so I tried to design characters whose personalities and ages aren't immediately obvious from their images alone.
Q: So, you're saying the "android" factor weighs most heavily in your designs?
Yeah, I guess so. When I first got Miku's specs, my immediate image of her involved headphones that would cover her eats and give her a more robotic look. I also wanted her to look even more mechanical than she does now. But over time, I toned it down a bit...
Q: What material did you intend for Miku's arm covers to be made from? Are they plastic? Metal?
I have no idea. The material for the arm covers is unspecified, but it allows the characters to move freely.
Q: If they're androids, do they have other robotic parts?
Well, I suppose you could say Hatsune Miku's hair ribbons are like that. I actually designed them to be free-floating. It could even be the case that her ribbons themselves turn with the tempo of the music (laughs).
Q: Those are the sort of props that make cosplayers break into tears (laughs). Though the characters are all androids, they have a very human cuteness about them, I think. Was it difficult for you to draw so many detailed parts for them?
I have my own less-complicated version of them in my head which are much easier to draw, but when it comes to the official designs, it's really no trouble. Though I have to say, sometimes drawing those belts can be a bit of a pain in the ass (laughs).
Q: Is there anything you're particularly detailed about when it comes to your artwork?
Wrinkles in clothing and lighting. Most of my illustrations involve gothic-lolita fashion, so I'm really careful with wrinkles and creases. Beyond that, lately I really love drawing Miku's twintails! Actually, I had originally intended fr a different hairstyle completely, but I tried out the twintails first on a whim and there was no turning back. At the same time, I decided to add the "01" to her arm and the arm panel detailing.
Q: Miku, Rin and Luka all have numbers on their shoulders along with their names, right? Does Len have the same tattoo or not?
He does. You can't see it because of his sleeve, but he has it on his left arm just like Rin. Also, if you look at my SD illustrations of the characters, you'll see that the thing slung over his shoulder in the official designs is a shoulder keyboard.
Q: How did the design for Megurine Luka come about?
Well the order came in for a 20 year-old, billingual female voiced by Yuu Asakawa. Her voice was husky and a little airy and she had been programmed to handle moodier genres like jazz. The image I initially had of her was of a more mature Oriental-styled woman in a traditional Chinese dress. The other impression I got was one of asymmetry (imbalance between right and left). Since she can sing in both Japanese and English, I wanted the impression of her look to be slightly different when viewed from different angles to capture that visually. I'm often asked about her eyes. I wanted them to be more mysterious and unreadable than Miku, Rin and Len's.
Q: Is there an equipment or instrumental basis for Luka's design too?
Just like Miku, Rin and Len, she has a YAMAHA equipment motif, but she also incorporates brass and woodwind instruments. Her own synthesizer motif involves wood-panelling that mutes the cyber-look a bit, so I think her design is a bit less "robotic" than the others.
Q: What about the jewel she wears at her throat?
It's tied to the intrument motif. I put a woodwind instrument motif along the slit in her skirt. Luka's whole concept is based on the idea of a "breathy voice". Knowing that, I developed the image of air moving through her like an intrument. The jewel adds moisture to the air passing through her throat.
Q: Of all of the different themes incorporated into Luka's design, which did you focus on the most?
The impression of brass. I didn't need to create the same metallic impression with Miku, Rin and Len, but with Luka, I had to worry about creating the impression of real brass. I tried to make her costume add balance to the whole character vocal series.
Q: So, which character in the series is your favorite?
I love them all, but I suppose the first, Hatsune Miku, will always have an extra-special place in my heart. As for the software, I don't really use any of them, so I can't say.
Q: Finally, do you have any message for your fans?
Please take good care of Luka and keep on using Miku, Rin and Len!
Thank you for answering so many questions for us today!
The source happens to be in English, as I couldn't get the translator to go away. Oh, well.
On another note, The original interview had images of their boxart, but not the actual characters' full bodies. I included those because PhotoBucket says you have to have a ProAccount to see them(even though they were fine last time I found that interview). So I replaced those images with full images of the VOCALOIDs that let you see the extra details and still made it easy to follow along with the questions. Luka's is a bit smaller than Miku's or Rin/Len's.