echoing a lot of the sentiments already so nicely expressed, but when you genuinely feel the excitement from the other person you're rping with. it's fun when a song lyric, meme, or random pic reminds you of what's happening in a thread or who the other character is and you can send it to them without feeling like you're the only one really excited. it becomes more reassuring when they do the same in return.

i think more recently for myself, it's nice when your character's name is dropped in a thread you aren't even involved in, but you are following. it's validating when it shows that your character is thought about outside of your own threads and that everyone is in the same world, setting, and what have you. makes me feel warm and fuzzy inside.

^{also going to include the bouncing back and forth of a thread and the sheer excitement from knowing how you want to reply and wishing you could even if you're just about to go back to work after a break!!}