Start with a moment, not a biography
Pick the companion whose point of view feels interesting, then open a scene with a little pressure already in the air: a missed train, a strange voicemail, an unfinished song, or a map with one detail that does not belong.
Give yourself one useful choice
Early decisions work best when they are concrete. Ask a question, follow a clue, change the setting, or tell the character what you notice. A small action creates more momentum than trying to outline the whole story at once.
Let the conversation continue the scene
When an opening chapter ends, you can keep talking with the character in the same story context. Use the chat to test an idea, learn what they are hiding, or decide what happens when the next chapter begins.