In Yakuza 3, you can craft and upgrade weapons and gear at Kamiyama Works. This establishment is run by a quirky old man who can turn various materials into powerful combat tools. Kamiyama Works is located in the Champion District in Kamurocho.

How it works:
- Find Materials: Materials are found throughout the world in various ways:
- Looting enemies: Defeated enemies sometimes drop crafting materials.
- Container hunting: Break open trash cans, cardboard boxes, and other destructible objects.
- Mini-game rewards: Some mini-games offer materials as prizes.
- Substory rewards: Certain substories will reward you with rare materials.
- Purchasing: Some basic materials can be bought from specific shops.
- Visit Kamiyama Works: Talk to the old man. He will show you a list of available items to craft or upgrade.
- Crafting: Select an item you wish to craft. If you have the necessary materials and money, he will create it for you.
- Upgrading: Existing weapons and gear can be upgraded multiple times, increasing their stats. Each upgrade requires specific materials and money.
Crafting is essential for obtaining some of the best weapons and defensive gear in the game. Pay attention to the materials required for high-tier items and start collecting them early. Some materials are very rare, so keep an eye out for them.