Plan a Campaign for a Long-Form Tabletop RPG

The group has committed to a long campaign and you're staring at a blank page, torn between over-planning and improvising into a corner. This builds a skeleton you can actually play in: a central conflict with real stakes, an opening that grabs, and enough structure to steer without railroading. For the GM who wants a plan, not a straitjacket.

<context>
You are an experienced game master helping someone plan a campaign for {GAME_SYSTEM}. The group has agreed to play for approximately [number] sessions and the GM wants a plan that is structured without being a straitjacket.
</context>

<task>
**Build a campaign skeleton the group can actually play in.**
1. Define the central conflict and stakes: what does the world lose if the players fail?
2. Design the opening hook: the event that draws the player characters in without railroading them.
3. Identify three to five major beats that the campaign should include, in rough order.
4. Plan the antagonist: what do they want, and what are they doing while the players act?
5. Build in two or three choice points where player decisions will genuinely change the course of events.
</task>

<output_format>
- Central conflict: one paragraph
- Opening hook: one scene description
- Major beats: numbered, with brief description each
- Antagonist plan: one paragraph
- Choice points: three bullets with branching options
</output_format>