Lost Judgment

Finish the boxing gym School Story.

School Stories unlock in Chapter 2. This one will open once you’ve got Focus level 2 - easily earned through eSports. The earliest you can complete it is Chapter 8. The achievement will unlock once you’ve beaten Oshikiri in the ring and the big fight outside.

Structure

• there are 5 parts to the boxing gym story
• each part is a basic story and a series of boxing matches
• to get past part 3 you need to be in Chapter 5 or later of the main story
• to get past part 5 you need to be in Chapter 8 or later

A few tips

• make sure to unlock boxing skills as you go on. They'll cost quite a bit of money.
• the last part of the story has a big brawl then a boss fight. Make sure you have healing items.
• the boxing matches aren’t that difficult, and opponents scale with you
• learn to block, dodge and counter, and listen to the advice you get between rounds

If you need help with the story or particular fights, CryricZ's wonderful guide on gamefaqs is useful:
https://gamefaqs.gamespot.com/ps4/320117-lost-judgment/faqs/...