1. Do we limit ourselves to how the protagonist found him/herself in the given situation and why s/he must escape? Or can we say how s/he escapes?
2. Can it be narrated in the first-person?
You are to write an origination story of how your protagonist found themselves at that location, as well providing the elements of why he/she must escape that situation.
These are the only base requirements necessary (How did they get there and why they must leave there) -- Anything else you wish to add i.e. the actual escape etc is completely up to you. The reason those two requirements are stipulated is because in Game writing you do not always get complete control of the creation.
You can use any perspective or presentation style you wish - for example you could do this as an Ode or a screenplay or from the viewpoint of the parasitic head attachment that the protagonist has not yet noticed....
I look forward to your submission :)