Sakura didn't really know much about her grandpa. She knew he liked stories, especially Greek ones. She knew he was strong and dangerous. She knew he didn't really like people. That was all she knew, and all she expected to know after her grandpa disappeared. Then she heard them; voices that claimed they knew him. They were happy to tell her all about him and make her strong too. (Been kicking this idea around in my head when I realized that Sakura having a sentient voice in her head should not be treated so casually and my Dream SMP brain was like "hah, idea")