AI training in my data

an artificial intelligence model that will be able to load all my data (a book) and will be able to answer through the book about the topics of the book (the topics are from a historical period), but will also be able to answer general questions, naturally always impersonating a certain person.
I have no problem using another API model as long as it can load the entire book and doesn't charge much tokens, also works in multiple languages.
I will be using within Unity 3D.