That sounds like an intriguing start to a story! It seems like you're setting up a scenario where the protagonist (or possibly the entire world) is facing an unexpected and unfamiliar phenomenon - an invasion of "reply girls".

To help me better understand the context and direction of your story, can you provide more details or hints about:

1. Who are these reply girls? What do they look like, and what's their purpose?

2. How do they seem friendly? Are they attempting to communicate or coexist with humans in a way that's unusual for invaders?

3. Is there an underlying theme or commentary that you'd like this story to explore (e.g., societal expectations, cultural differences, power dynamics)?

4. What kind of tone are you aiming for - humorous, serious, sci-fi, fantasy, or something else?

Feel free to share any additional details or insights you have about the reply girls and their invasion! I'm here to help you develop your story.