There's the trope Commuting On A Bus where a regular character is downgraded to a recurring character (often due to an actor not being able to be on the series full-time). But what about its opposite?
There are occassions where a recurring character becomes a regular character on a series (possibly to fill in the void left by another regular cast member's departure). The two examples I'm thinking of are Hailey Upton on Chicago P.D., and Brainy in the CW's Supergirl. Both of them started out as recurring characters, and became regulars after other cast members left the show.
I'm sure there are more examples out there. So, does either this site, TV Tropes, or both, have a trope for this?