Yakuza 3 Remastered

This achievement will require you to go fishing out front of Morning Glory but first go to the public market in Okinawa and buy 10+ shrimp bait just in case you don’t get lucky. Then go back to the fishing rod on the beach in Morning Glory. Keep entering/exiting the mini-game until fish spawn in the 140-150m range (Tuna will only spawn at that range). Cast your lure with shrimp bait ensuring it lands on the fish in that area. Don't touch the line and wait until A appears (it may take a few tries). It appears for less than half a second so be focused on that prompt.
Once you've hooked the fish, it'll take 2-3 minutes to reel it in. Ensure the line doesn't go above 75% tension and point your rod in the direction the fish is moving (left or right). Just be patient and don't rush it while keeping an eye on the tension meter.
Also, note the tuna you catch can be used for the sea bream sub-story so I'd recommend hanging onto it until then if you already haven't just paid the 300k for it.
Here’s a video of when I got this achievement:

So, to get this achievement, you first need to purchase several units of shrimp bait, available inside the Public Market on the southwest corner of the first floor map. Shrimp is the only bait that attracts tuna. Second, before going to the fishing rod at the beach to start your minigame, save your game at the save point inside the Morning Glory house, just in case you fail in your attempts and end up running out of shrimp bait with nothing to show for. Then when you load up the fishing minigame, focus only on the last third of the distance gauge (between 100 and 150m) bar when finding fish icons, as that's where tuna are located. If no icons show in this area, just back out to the main game screen and load the minigame up again, as the layout refreshes every time. Once you get a fish icon in that 100-150M range, cast your shrimp bait and time your input to where the red bar lands on the fish, with an emphasis to the head. Then, just wait until the button input pops up as the tuna catches. You only have a half-second before the tuna breaks free, so timing is of the essence.

When you make your catch, just pull the rod with your left thumbstick to follow the direction the fish is going, by doing this, you reduce the tension on your reel. Press the button only while your rod is in sync with the direction of the fish and while the tension bar is in a blue or green state, letting go when that bar is halfway filled (yellow) or has gone red. This can take anywhere from two to four minutes depending on your proficiency with the fishing minigame (I had caught only one other fish prior to my tuna catch). It all comes down to patience throughout the ordeal.

What you want to do with the tuna is up to you, but since the tuna is the item in question that's necessary to complete the Sea Bream Strongarm substory, then it's more likely than not to serve as priority.