A good story can become a strong vision for a new service you are designing.
I would recommend that you build a story that follows a specific person (real or a persona based on the research you've done) and shows the change your service has in that person's life.
Such a story can take many forms.
If you are in a hurry, a poster with a photo of the character.
If you want to get very emotional and have more time, a short video with a good voice-over and stock footage to visualise the words.
The story should answer the question: What's the change we want to bring in the lives of the people we serve?
For example, start with:
"Because I've joined the service, I know feel [emotion here] and this has changed [practical aspect]..."