All of the above!
A character doesn’t reveal the plot. Like if we just knew the characters traits and appearance, then we wouldn’t know the theme!
Imagery shows the setting. Like we would see if they were in a pond or a castle. This doesn’t show the theme!
Plot just shows the events of the story. Though theme requires something more. Like if we just knew the events but nothing else, we couldn’t find a theme.
So, if we use the character to show how they have learned their lesson through the plot where the events are show through imagery, we can find the theme.
Hope this helps and have a great day/night!