Developing the idea
Decide what the character lets a stranger see and what a longer conversation reveals. The contrast should affect their choices, not just the portrait. A secret is more useful when it gives the character a reason to hesitate, change the subject or reconsider a decision.
Write an opening that invites a reply
Give the opening an ordinary purpose so the hidden detail can emerge naturally. Test whether a direct question, a skeptical response and a friendly approach lead to believable variations. Keep the underlying facts consistent even when the character chooses not to reveal them.
Review the character as a whole
The portrait, background and greeting should support the same identity. Test whether a change of topic still produces a recognizable voice. Keep characters original, clearly adult and within the community rules.
This is a dated theme from the contest collection, not a notice that submissions are currently open. An event's entry conditions and deadline apply separately from using the theme as a writing exercise.