Neir has the best fishing mechanic of any RPG. You hold down a button once you see the rod dips and move the stick left and right. Either you get it or you don't. Never had any trouble until near the game.
I used this from a faq
"Odds are, you tried to tackle the fishing game on your own at first, and odds are you absolutely hated it. Thing is, the in-game explanation for how to fish is absolute garbage. Forget it. Nier's fishing game is deceptively simple--almost too simple.
Here's what you're doing: you press cross (or A) to cast your line. Don't worry, it's not supposed to go very far and you can't alter the distance. Watch the tip of the fishing pole. It will bob up and down a few times. Wait for it to bend down further than normal, and press cross--and hold it. You are now reeling the fish in. This is where things get tricky: the fish will swim from side to side. The protagonist will automatically move his body in the opposite direction of the fish--you cannot control which way he moves. What you need to do is to pull the move the left analog stick along the exact same angle as his body. If the protagonist is standing still, pull down. If he's pulling to the left, you pull to the left, and vis versa.
The red bar at the bottom is the tension meter. So long as it's red and making that lovely clicking sound, you're doing fine. If it turns yellow, you no longer have the analog stick in precisely the right location--shift it until it turns red again to reel in the fish.
Like I said: deceptively easy. You can increase your fishing skill by completing the, "Fisherman's Gambit," series of quests. Fishing skill effects the amount of time it takes to reel in different kinds of fish. The lower your skill, the longer you'll be reeling."