I can't say I see much in the way of NC-17 stuff here. Is there going to be more that would qualify as that down the track (possible given he mentions taking on TR), or just an over-rating? If the former I'll suggest keeping things in check with the rules (some sort of stuff we're not keen on allowing in fics on these forums) but atm that's not going to be a concern. And if the latter is the case then maybe a more fitting rating should be considered.
But the more concerning thing I think is the way the story is presented visually. At the moment it appears as one large paragraph that's also centred to boot. You want to break it up in separate paragraphs, in part as it's a fairly solid rule to follow with writing to begin with and also that it's very hard to read as-is. It is easy to get lost with where to read from, and stories on computer screens isn't the best thing on the eye to begin with. Centreing the text is also unusual and not something the typical reader will be used to, so I suggest reverting to normal formatting so it's more presentable.
Otherwise the story has a not-bad start; it's just hard to go through it without the proper presentation (look at it this way; people will tend to go through with reading a story with proper paragraphing than without due to ease of reading).
A few story-specific comments:
- Try not to start sentences with 'I ____' too often. It's not so easy to do with first person stories, but it can lead to a repetitive tone in the story. (I ___, I ___, etc - more like a list of events if overdone.)
- Numbers less than 100 are typically written out in word-form (so say thirteen rather than 13. #1 can be an exception to that though, mind).
- 'Fins had grown on it’s skull and legs' - it's means it is, while its is what you want (the possessive form, eg its ball rather than 'it is ball').
- Watch out for run-on sentences (like 'I managed to sit up and catch my breath, I looked around to make sure nobody was around.' - if they could work as separate sentences than it is better to keep them as so rather than just join them up with a comma (which can be grammatically incorrect too).
- All in all it's a decent introduction to the story; there's a setup of the world and some motivation for the character too. I have a few questions about it here and there but perhaps that will be resolved later on in the story.