Mostly out of shame over his broken horn, Kimahri rarely speaks to anyone. When he does, he only talks to those he likes and trusts, which is a main part of why he does not initially talk to Tidus. The first time he speaks during Final Fantasy X is following Operation Mi'ihen, when he reminds Tidus—who is shocked to hear Kimahri talk at all—that he must keep a bright exterior and happy face to help brighten Yuna's journey. From then on, Kimahri only talks when necessary and usually offers helpful advice when he does speak.
Despite his frightening appearance, Kimahri can be gentle and kindhearted. He gets angry quite easily, but he always directs his anger towards those who threaten his companions. He's also fully dedicated to Yuna's safety, and is usually the first to be around when Yuna needs help. He doesn't hesitate to show his strength to others. This is further hinted by his resolve to reclaim his honor from his people.