What is the world situation? Is this a future/alternate earth, or some other alien world – with a human colony or some other alien race? Are the Mechs sentient or piloted by a being? Part of an alien technology or domestic? Part of a “home defense” network or an invading force?
Then there’s the soldier with the hostage: Resistance fighter? Invader? Liberator?
And the hostage: What’s her story? Is she a native or colonist? Why is she outside? Is she truly being taken hostage, or simply sheltered from the Mech?
Now, I’m going to ask you to think about story structure: would you consider this event as a short story or as a major incident in a longer piece? Whose story is it? What events lead to this moment? Where does the story go from here?