Derrick Gibson
We're still trying to figure out what's up with Derrick Gibson (Rome Flynn). The character has some demons to deal with, as evidenced by the manslaughter story he shared with Carver (Jake Lockett), but the show is making it seem as though his time with 51 is coming to an end.
To be clear, Gibson joined the team the episode after Gallo left, so he's barely clocked any screen time. While extenuating circumstances are always worth taking into account, it would be bizarre from a sheer narrative standpoint to introduce Gibson and then immediately axe him.
We hope to get some clarity on his character soon (especially if he's on his way out).