Here I will discuss briefly what each of the Key franchises’ titles have to do with the plot/theme/motif/etc.
Kanon: Canon is a series of events such as memories that happen, MC has been to this town before in the past but only remembers bits and pieces of it
Air: I think this is a pretty boring title since a lot of things revolve around birds and feathers
Clannad: A clan is a family, main theme of this story is about the importance of family
Planetarian: it takes place in a planetarium after all
Little Busters: busters mean something broken in this case there was a bus accident; the MC and Rin are also broken in that they are unable to deal with the situation so Kyousuke made the world
Angel Beats: Kanade is called Tenshi which means angel, After the MC died irl his heart was given to Kanade
Rewrite: The power itself is called rewrite
Harmonia: I think this has something to do with the music box
Summer Pockets: We are trapped in an endless summer and pockets means memories of that summer
