Okay then, The most important part of the logline and story would be the games opening event.
This will also be your characters call to action.
What compelling event happens at the beginning of the game that calls the Character to his course of action to defend Avagon?
In logline terms, you would open the logline with "When (This compelling event happens) a brave huntsman must defeat...)
For instance in Skyrim; the opening event is the return of the dragons,?
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"When Dragons return to ravish Skyrim, A prison?born on a certain day, under a certain sign, must travel to High Hrothgar to learn the ways of the voice to defeat the Dragon menace."
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So I would look at the opening of your game and ask what compelling event sets your characters path and then use that event to begin your logline.