Coming from a Polygon interview with creative director Patrick Plourde...
"I'm a father, and fairy tales are about parents telling their children stories that carry values. So one day our marketing director said, 'Why don't you make a game where you can play with your son?' and I was like, 'Ah! That's so true!' It's fun to share an adventure. Ni no Kuni is a great game, and it looks like it was made for the whole family, but you're playing alone. You can't be with your son or daughter and play together because it's only single-player.
So I had the idea of what if we took the Super Mario Galaxy approach where you have a character that helps? What if he could move around on the screen and it's not a nuisance for the parent? But the thing I felt was missing in Super Mario Galaxy was the second character is not really helping. You just collect coins. It's not a collaboration — you're more of a spectator.
Watching sports with a child, when the team scores a goal then daddy's happy and the kid is happy, then we're giving each other high-fives. You should have those moments with games. It's good to share moments and it can be with a child or it can be with anybody."