"That might be one possibility, though maybe not loneliness exactly." Sakura shook her head "Since he loves his brothers very much and his adoptive father loves him very much too.
I think it's more of him experiencing what my father calls 'culture shock', he grew up with the Dwarven culture all his life, but he doesn't know too much about other cultures, and neither do the Dwarves. My father experienced a similar sensation when he first came to this land, though some things were similar to him they were also very different. I certainly still experience culture shock since there are many things I don't know about, things I desperately want to learn. But 'Human Society' is something he just doesn't understand quite yet, and our customs for that matter. I only know what I know because of my father, because he always told me what Society was like. The Dwarves and Riagan don't unfortunately.
In fact before this happened we were planning to leave the forest and travel the world to find a different place to live in 2 years, he wanted to make sure I would be ready for the world before we did. But Aya and the danger seems to have accelerated those plans.
As for his 'scary fighting' I think it has more to do with how those people harmed his brothers. That Doll Woman possessed some of them to fight us and Shadow Master and Mask Master killed others. Kidnapping Aya was something he was also very angered about, he has a sense of justice. I can understand how he felt, I too was very angry about what they did.
But I think he was consumed with venegence because of their misdeeds and transgressions. That venegence blinds him so much that he can't think about much else unless you point him in the right direction.
I think Riagan, and quite possibly the Dwarves in general, are more suffering from 'stunted growth', as if they have a narrow understanding of things they aren't familiar with. They don't have a 'Worldly View' so to speak because until now they didn't need to have one.
I think perhaps once Riagan learns more about what's out there maybe he'll change a bit. Though it would take a long time, and we shouldn't force him. Same goes for the Prof as I learned, as surprising as it is they are more similar than the other might think.
At least those are my theories."