I don’t think I’ve ever friendshipped a guy and a girl this hard before. Dean/Charlie comes close, but it’s a bit different because Dean and Charlie don’t canonically see each other that often (even if they practically live at each other’s houses in 60% of the fics I read) and Sherlock and Joan live together. There’s a lot more opportunities for feelsy friendship moments this way.
I just. Joan went without pay for like three weeks because she didn’t want to move on to her next client, and Sherlock wanted her to stay so much that he didn’t realize she’d lied to him- he had to find out from his dad. And when he invited her to stay on permanently… you can just tell how much he wants her to stay, and you can guess he’s never felt this way before because he’s never had as good of a friend as she is.
And he’s teaching her how to do deduction stuff and everything.