Beyond the main story antagonists, Yakuza 0 features several hidden bosses that offer unique challenges and rewards. Additionally, secret trainers can teach you powerful, often unconventional, techniques that aren't part of the standard upgrade trees. Seeking them out is essential for unlocking your characters' full potential.

- Amon Clan: The ultimate hidden bosses in the Yakuza series. Defeating them is a true test of skill.
- Secret Trainers:
- Komaki (Kiryu): Teaches powerful counter-attacks and defensive moves.
- Sotaro Komaki (Majima): Teaches unique Heat Actions and evasive maneuvers.
- Other Trainers: Look for specific substories that introduce other unique trainers.
- Unlocking Conditions: Often tied to completing specific substories or reaching certain milestones in mini-games.