Keima would be classified as a young adult, and Nu is close to being a young adult, but I get what you mean. What I mean is a character younger than 13. Someone with very little to no judgement, barely knowing what's right and wrong, and really just having to cope with taking on serious responsibilities and growing up mentally in that process.  

I caught myself on the verge of a pointless tangent there. Not going into that territory though.

I just noticed something. Is the way you're spelling Tokyo intentional? With Tyoko. Or is this just a fantasy version of Tokyo, that's not actually Tokyo but may as well should be?