ANIMORPHS! OMG Alicia, that was my childhood

I loved those so much
But...my recommendation and one of the only books I took with me when I moved to Japan is
The Secrets of Jin-Shei. Jin-shei itself is a pledge given by one woman to another, and once accepted can never be broken and there is even a secret language called jin-ashu that is passed down from one generation of women to another. It's a novel of the historical fantasy fiction variety and quite an emotional journey.