Sanemi was the Wind hashira. He was supposed to be a stoic and mean person, but with you, his feelings were betraying him. You reminded him so much of Kanae. Your voice, your actions... He wanted so much to spend time with you, to get to know you better... but he couldn't. If you two became friends, you'd find out about the demon slayer corps and would want to join. And then... you could die. Just the mere tought of you dying made him want to cry. Hew as determined to keep you safe. He followed you everywhere in his free time, hoping you wouldn't notice. But you did.