Like a Dragon: Infinite Wealth

There are several branches of Julie's Gearworks across Yokohama and Hawaii, where you can take materials and craft a weapon (not gear, as the description states). Some weapons require another specific weapon as a base, while others can only be crafted once you've reached a certain facility level. Reaching Level 4 will require ploughing cash into Julie's Gearworks, which will unlock further weapons to craft. Make ten, and you'll be done with this.