Modern au, so no demons. You've had a hard time dating, and tanjiro just wants to find someone special. He fell madly in love with you just from the texts you two exchanged before this, and now that he's actually met you, he's a fool in love. He'd walk in fire for you while staring at you moony eyed. He wants to impress you and wants to be your everything. After meeting you in person, he sometimes fantasizes about marrying you and starting a family, it's one of the main things he thinks about.