I actually thought about just adding the info to each of its respective game's sections but maybe one long one is for the best. So this is some of what I've learned for each respective game so far.
DMC1:
Griffon is supposed to resemble
Roc.
Mundus killed Eva and retreated to Mellet island to plan another invasion of the human realm.
Griffon's many faces were an idea that came from the days it was aRE boss.
Nightmare was originally an ancient virus that would hatch and parts of the eggshell would be mixed in there. That and it would shoot missiles. Yeah, you read me right, and the artist was just as confused.
Kamiya originally intended for the game to not have a jump function but the staff talked him into it. He wasn't happy about it but in no time not only was he into the idea, he also wanted to add a double jump, which is where the push for a jump backfired on the staff because the environments were not meant for it and even worse, Kamiya now wanted a 'flying' function to the DT.
Mundus appears as a god but that is an intentional choice. He has another form that is the 'real' one, a pitiful real form when he starts to crumble.
The Blades and Frosts are meant to be able to shoot their claws but the Blades are meant to look like it's a painful act, that is hurts to do it, unlike the Frosts.
The data for the final version of the game that was sold on retails was lost and the last built that was saved as a backup is an earlier model which is why DMC1's Dante costume in 3 had to be built from scratch and the DMCHD version of 1 was so... raw.
Most of the people working on Dante's character didn't know what kind of character he was. They thought he might've been a nihilist, just on appearance alone, and the fact that he was half demon with the ability to turn full demon added to this 'dark' view of Dante. One of the people interviewed mentioned how he first realized what kind of character Dante was when he saw the Phantom scene.
I already mentioned this but after the title was changed to something not Resident Evil but still featuring Tony Redgrave the working title was 'Karnival.'
From the beginning Trish was meant to command some kind of element. It wasn't set in stone if it was going to be fire, lightning, or something else but I got the impression that her blond hair made it obvious that it was going to be lightning.
Tony Redgrave was British and was always going on about 'the goddess' which was either the goddess of luck or his goddess, England.
Very little from the Graphic Edition and Graphic Arts books have actually been put in this book so there is a lot of basic stuff been unsaid. If you haven't read it before go
here and
here for more on DMC1, specifically.
DMC2:
Dante wasn't really going to be the original protagonist, dude in green jacket, blah blah blah.
Lucia is actually a rather sweet girl but time constraints prevented any additions of scenes that would show her softer nature and the staff was disappointed they didn't get to show it.
The staff pretty much got free reign to design but it sort of caused a disorganized situation and Itsuno was hired as assistant director by name only and as full director to finish the missing assets of the game, which included all the cut scenes since they hadn't even been filmed, and put together what was already made, the game was do out in six months and he wouldn't get credited for it.
Arius' face is partly an homage to Lee van Cleef, the villain from
For a Few Dollars More.
One of the producers, Tsuyoshi Tanaka, used to work for Dissel right before he got hired at Capcom so he used his connection to make the collaboration happen.
DMC2 takes place 10 years after DMC2, making Dante around 30. Among the staff they aren't exactly sure where it fits in the timeline, they even joked about how it might take place in an alternate time line.
There was a time when Matier was going to be a man but an old woman contrasted better with Dante as a mentor type.
Despair is a hermaphroditic being which is a symbol of perfection in alchemy, a mixture of opposites, just like an eclipse (I actually knew all that already, thank you moseslmpg, but in the book they call him androgynous, not hermaphroditic). A perfect, everlasting being, filled with endless energy, like the sun.
The Trismagia is a mockery of the three wise men of the Christian creed.
Lucia was made specifically to be ethnically different from Trish and Dante. The interviewer said she had a distinctly 'South American' look to her but she has no specific nationality. French never came up.
Itsuno mentioned that DMC2 was actually well received. Fans of the original didn't approve but people who found 1 too hard or hadn't played it were happy with 2 according to many resumes and fan response studies.
A lot of the staff saw how DMC 2 was turning out and that in turn drove them to deliver a better experience with DMC 3, to give it their all.
There is very little new when it comes to 3 and 4 but here's what I've seen so far.
DMC3:
Jester is actually a consequence of the failed ritual Arkham performed when he killed his wife, a split personality he obtained with the power he gained from it; Arkham isn't powerful since the ritual failed, so the power to transform in almost the only power he has. While Arkham has a clergyman motif he has that twisted side, which they wanted to make as contrasting as possible to that view.
Dante was always going to be bare chested. They wanted to show off his physique and were inspired by a Japanese band named the Johnnys.
The game was designed with a very specific appeal to the Japanese market so when characters, specifically Vergil, who has a Katana and very Japanese appeal, became popular everyone was surprised and proud. They talk about it as thought it was affirmation of all of their hard work.
Nevan was a sorceress, a rather apt one, who was sealed away by Sparda.
Leviathan is a biological weapon created by the demon emperor. His insides are connected to the hell of envy.
Originally Lady was going to be older than Dante. She was going to be a cigarette smoking demon hunter who could act as a mentor type but Itsuno said the only way she'd be popular with the Japanese players was to make her look like a high schooler.
Originally the devil arm would transform as well when Dante DT'd but time restraints.
The staff put their all into DMC3 and Itsuno was going to move on to a different game when they were finished but most of the staff was made to work on DMC4. The problem was that they were all burned out on DMC since they put so much effort into 3.
DMC4:
It was the fact that everyone had given their all to DMC3 that they wanted a new protagonist for DMC4, because they couldn't go on with Dante anymore. Itsuno thought that a new protagonist would bring some re-invigoration to the staff, who was struggling to get off the ground when they started the project.
Nero went through several character types. The first was that they wanted to make him a Sherlock Holmes type gentleman who drank tea when he fought demons. The idea was obviously not going to work so they moved to a more savage type character that struggled with his demonic side. Eventually they had to settle with a very Dante-esque character with some significant differences. They mentioned that Nero would just be like Dante if they aged him 10 years in appearance but what about personality. The example they gave was would Nero be the type of character who covers up when he's at a public bath or would he just let it hang. As opposed to Dante, who'd feel no shame at let it all show, Nero would be the type to cover up, he's a more reserved young man.
Kyrie was always a Virgin Mary type of character who was pure and kind, with a very complicated relationship to Nero as older sister, mother, and lover all in one. She was supposed to be sexy and curvy with a large rack but also the embodiment of religious devotion. Someone suggested giving her a dark side but got shut down by Itsuno pretty fast. It was said that the story would have her as a damsel in distress and a cookie-cutter big sister type. The keywords for Kyrie are 'kindness,' 'self-love,' 'caring,' and 'compassion.'
They make a notion of how Nero is actually a lot like Vergil and the only link he has to humanity is Kyrie. He only joined the order to protect the city Kyrie loves, not because he has any attachments to it. If Kyrie hadn't looked like she was in danger when Dante was near him he wouldn't dropped kicked Dante, in fact, he would've put on his headphones on again and walked away with a 'none of my business' attitude. They went as far as to say that if Kyrie died Nero would probably just go down to hell seeking power.
To show more of that wild side of Nero's originally he was going to get more savage near the end of his combos.
Credo is balding. Seems kinda obvious but I always just thought he had weird hair but I guess he's just losing it.
Credo and Kyrie actually share some facial feature.
Agnus' stutter was suggested by the voice actor.
They had a lot of issues with Nero's design. It seems that it didn't matter how much bulk they added he just looked thin and almost delicate.
Dante was going to have a second stage DT but nothing came of it.
Credo was supposed to be the final boss but because that would drive an un-fixable wedge between Kyrie and Nero they went against it.
DmC:
Apparently they think that out of all the characters Vergil saw the least amount of change. Originally they wanted Vergil as a cold blooded killer with OCD; If he got a little blood on his glove he'd toss it immediately... And apparently they wanted to make him more of a pervert, too.
The entire theme of DmC is rebirth and there are a lot of elements that reflect that.
Mundus was all NT. The way they see it is that's how NT thought of demons, heavily human, comparing him to demons they look in Constantine.
I'm sure there is more but I'm a bit exhausted typing this out. I'll just leave it there.