I read this book in the mid 90s and for the life of me I can’t remember the name of it. Here are some things that I think I remember although I’m not 100% sure.
The author is either of Native American descent or if not there are Native American themes in the book.
For some reason I think there might be the word “black” in the title.
This was a book with two central protagonists, one young boy, who went on a journey, found a sword that would telepathically speak to him, and some sort of princess-like character. The only detail I remember about the story is that they would regularly refer to "heartstrings" - almost like the HP bar of the characters. The swords would strengthen the heartstrings of the people wielding them. The person holding the sword could take more damage and still live as long as there were still these “heartstrings” between the wielder and the sword.
There was a river involved who was the antagonist. The boy went to the head of the river and poured something into it which flowed down the river and killed it/wiped away the evil/badness.
That’s about what I remember. I believe there was a second book and possibly a third but I need to find this first one.