Not too bad of a challenge as long as you're patient and whittle his health down
A couple of little things to note:
I wouldn't recommend doing this until you've upgraded your max health a few times
Make sure you have plenty of healing items
One of the harder parts of this achievement is simply finding him. I personally have no idea of his spawn points so you'll just have to get a bit lucky
There is an upgrade you can buy at the Shrine that will increase his chances of spawning in the park. It's not an ideal place to fight him but it can be done there. It's actually the place where I got this achievement
I also recommend finding the nearest save spot when you get in sight of him just in case you lose the fight so you can reload your save without fear of losing all your money. Another thing worth mentioning is that you cant keep reloading a save if you do find him as he will be somewhere else when you reload the save. So you cant trial and error him by continuously reloading your save and retrying
As for combat I simply ran circles around him and keeping track with the free cam. He has an attack where he'll charge you and another where he will throw punches. They're pretty easy to bait out whilst keeping a good distance away. Go in for a couple of hits and back away and continue circling him. I simply repeated that process with Kiryu using Thug Style. Its not an ideal method and can be quite time consuming but its how I unlocked the achievement. One last thing is that I don't think you can use Heat Actions on him because I don't think he can be grabbed. So don't go in for a grab and leave yourself in a position to get attacked.