I really do mean anything, I'm the type of person that prefers a more fluid approach to CR, like finding a reason for two characters to be in the same room and seeing how they naturally bounce off of each other, and what develops from that. But, erm, types of CR, let's see...

As I said, Armin doesn't have much of a purpose on Keeliai right now, so he could use a mentor-type character to guide him. He's also kind of mentally unstable, and I've always wanted to play him against someone who understands at least a little about psychology. While Armin can make enemies, he is generally on the side of "humanity" and as he is currently in canon (although I hope to update him soon) he is loathe to hurt "innocents" so you would have to be super evil to get on his shit list. So maybe negative CR would be difficult to make.

But even just something as simple as a friend is fine, he kind of... doesn't really have any close friends anymore, though he's trying to reach out.