Are you not supposed to play as Nyx? I have no idea where to go or what to do I keep roaming around the map and finding areas soft blocked by fog.
You need to find the faerie (just past the graveyard) who'll tell you about the key. The key itself is hidden in the grass near a tombstone (a pretty obvious one, at the very start IIRC), just slash it. Once done, after a long cave segment (boss included) some of the fog will fade and the small town segment at the very south will be accessible, you'll find a catgirl there who will hint you about each of the remaining objectives (she'll be there all the time so you can reach her should you get stuck). I have no idea how to progress after you make it through the scrapyard though, as all the exits are locked off with placeholders, probably that is the end as at some point the game just displayed the final stats screen.
P.S. About my own fishing question: the lure behaves different depending on the force bar, it is not as simple as "left is close, right is far". When somewhere in the middle, you do a strong low throw, which, unlike when catching the bar at the right, will allow you to hit the furthest chest (one that contains the tunnel key).