You're welcome, Hayabusa. Whatever help I can give, I'll give. Hey, and you're free to use any suggestion I throw out there.
In regards to a triangle, you could say that, like DeathEvan states later on, Katt, over the course of the journey (near beginning to onward), starts to look at Ryu in a different light, but doesn't let on about it openly, still uncertain about what she's experiencing. There could be subtle hints like a little flirtation here, her accidently(?) peeking on Ryu as he bathes there, and some nice rapport. The time were she may probably realize it's too late is the Tiga incident. She could be talking about liking him, but realizing that what's between them isn't love, though she begins to put the pieces together in regards to her feelings for Ryu. By then, Ryu and Nina would probably be pretty deep in their relationship, which causes her to be angry at missing her chance. How she reacts after that is up to the author. That's just my suggestion on this, though.
I think for Katt, it's all about discovery - exploring landscapes, trying out different foods and clothes, and falling in love and dealing with heartbreak/heartache (in regards to Ryu). She's learning and taking in everything since the fight is all she lived for.
I can try to give more reflections/insight in relation to your fic if you would like.