But what if this happens ...
Grell has a really bad day and she is also late so when she goes back to the reaper realm William is angry and tries to punch her with his schyte. Surprinsingly Grell stops him and is all like you are SO WRONG about ME and I'm not letting you touch me AGAIN!!
And then poor William is overthinking about that like all over a week, he is trying so hard to avoid Grell because he is sure that he lost his best friend now ... until Grell finally find him and gives him a biiig bright smile and asdjdbnak
Ok, this is not a normal romantic grelliam headcanon but if this happens it would be a HUGE step in grelliam relationship. William would be careful in treating her like someone instead of sometrash and also both of them would be happy with that.
Of course Grell won't stop being Grell xD