He's a cold heartless villain. You are basically a sunshine person. You're the sweetest person anyone has met and basically no enemies. No one has the heart to hate you. Tanjiro just so happened to see you when he was strolling around, out of his villain outfit so no one knew he was the villain, and he instantly fell for you when he saw your kind smile. It's a world where the heroes and villains have powers. A hero would sacrifice you to save the world, but a villain would sacrifice the world