What John says ...
A theme is an idea (or message) about life that an author wants to communicate to their readers. When it comes to theme, it isn't the characters or location that matter, it's the way the story is told.
So the same message can be delivered by a story that is set in the future and about robots, one set in the past about magicians, or even one about an ordinary boy's trip to the shops, set now, in 2010.
Here, Tiffany tackles something that is very important in all our lives: trust.
The robot delivers its message in a simple way: Iszuki asks Kary to trust him and, despite discovering he's a robot, she says she thinks she does. To me, this seems like just the start of a story, and the theme is told to us rather than being dramatised. The message of a story has more emotional impact if it is communicated by the actions of the characters rather than just through their words.
Also, this message would feel more powerful if it had been tested to the point of destruction. In life, we're more likely to believe in someone if they've overcome huge challenges to achieve their goals.
In A Robot to the Rescue, if Kary's trust in Iszuki seemed to have been totally destroyed by his actions, before being restored, maybe Tiffany's message would come across in an even stronger way.
Let me try and show you what I mean.