Following the steps in this guide will allow you to catch this elusive fish without too much stress or wasting too much time.
How to Cheese the Big Tuna (Maguro)
Step 1: Preparation
You will need proper bait to catch a tuna, either get shrimps from the Ryukyu fish market or use simple burger sets from Smile Burger (don't ask why tuna like burger sets), tuna's spawn at the 120-150m range, if you don't see a fish icon, simply exit and re-enter the minigame.
Step 2: The Cheese
Because this was a less-than-stellar port (sorry QLOC you messed up) you can abuse some settings to change the game speed, there might be other ways to do this, but here is the method I used:
- Change your FPS cap to 60.
- Raise your render scale until the FPS starts fluctuating around the 30 FPS mark.
- Your mileage may vary based on how good your system is, but keep messing around with the settings until you hit that mark.
When you cap the framerate, game speed will be tied to FPS, if you get the game running at 30FPS you will effectively make the game run at half-speed, immensively helping this mini-game. The first thing you will notice is that Kiryu will be walking very slowly, running it at 30FPS with a slow speed might be a bit nauseating, but it will help you A LOT catching tuna.
Step 3: Execution
Keep going in and out of the mini-game until a fish icon appears at 120-150m range (you are just going to have to eyeball it). Fish spawns at this distance are always tuna, use appropriate bait and hook it, if you used the half-speed trick properly the window for hooking will be marginally increased.
To reel him in simply hold RB (or the equivalent for your input) to reel it in, steer the analog in the direction the fish is going, push forward to decrease tension, and backwards to increase it. If the meter gets too high, use LB to release the tension, if the meter fills or empties out, the fish will escape.
Reeling the tuna in will take around 3-5 minutes, so be prepared to focus, the tuna changes direction constantly and erratically, the half-speed trick will again help your reaction time.
Doing this you should be able to get the achievement/tuna without too much effort, you can sell the tuna for a decent price or use it to complete a substory.
This half-speed trick might be usable on other mini-games, but I haven't tested it yet.