Hmmm, it’s a toss-up between Anne of Green Gables and Narnia. Anne, because she truly did feel like a “kindred spirit” and still does, but Narnia…
I got The Lion the Witch and the Wardrobe for free one year from Scholastic because I had ordered so many books! I took one look at the cover and the title and tossed it in a corner. It looked SO stupid. Cut to me a few months later coming around to it when I was out of other things to read and deciding to give it a try, omfg.
Everything about Narnia fed my imagination in the best possible way. I was too young to care about the allegory, I just loved the story so much and would not stop until my parents had bought me all 7. I lent my cousin my original copy of LWW because I wanted to share my favorite thing, and she abused it so badly that when she gave it back, it was unrecognizable. All bent and stained, and I absolutely bawled because she had hurt something that i loved SO much.
Is it my favorite now? No way, but as a child, that series definitely fired up my mind in all the best ways that a book can.
This is exactly what I came here to write, so thank you for saying it!