Personally, I don’t think there are any spoilers in the quotes below, as nothing specific is revealed about certain characters or events, but read at your own risk…
This information comes from director Kuniomi Matsushita…
“When the development team was making a prototype for the game, they came up with Chibiterasu with the idea that, hey, let’s make Amaterasu’s child. Seeing the character made me reason that, although he’s cute and everything, it’d take more than a child to save the world. That’s why we gave him partners to work with — together, they’re one, so to speak. That expanded the potential gameplay available, and I think it made the characters more engaging to players. The basic storyline and gameplay system went from there. There was a lot of debate on what to do before then. At one point we had five Amaterasus forming a party; we tried all sorts of stuff.”
“And because encounters and separations are such a big part of the theme, that’s why we didn’t want you to be able to switch control between partners. If you could switch between them any time you wanted, then they wouldn’t be partners anymore — they’d be tools.”
“We thought about setting it more like ten years later, but with that kind of space, a lot of things change in that time. We wanted things to be just a little different from before, so that’s why we went with nine months.”
“I saw it (killing one of the main characters) as necessary for the story’s flow. Okami had several key people die during the story, but none of them were characters the player would get very emotional about. For this game, I wanted a more important character to die in order to reinforce that ‘separation’ theme. There were a lot of people against it, definitely, but I discussed it with Kitajima and he said that he could see it working.”
This information comes from producer Motohide Eshiro…
“Having the story being about kids working together was very easy to visualize, comparatively. It might be partly because I’m a fan of the movie Stand By Me. That’s another story of kids going on an adventure and growing a bit along the way. Everyone’s had an experience like that, I think, and that’s what makes the story resonate with us. For example, maybe you moved out of town and had to say goodbye to your friends — but then you made friends with new people where you moved. Encounters and separations are some of the most moving things we experience in our lives, and I wanted to depict that in the game.”
“I do think, though, that we’ve been successful in really integrating the story with Okami’s. We could have made them separate tales, but I think fans would prefer having the two worlds linked together.”
This information comes from Yukinori Kitajima, Japanese novelist and the screenwriter for Okamiden…
“You’ll find out how that (Kuni’s birth and his age) happened during gameplay. I think it worked out pretty well plotwise, although getting there was a major headache for me, to be sure. I’d come up with some humorous backstory, but it’d always lead to contradictions later. What’s more, the last bit of Okami had Issun restoring humans’ faith in the gods and so on, and apparently it’s now all been forgotten in the space of a few months!”