Like a Dragon: Infinite Wealth

During your time as Kiryu in Yokohama and Kamurocho (there are several chapters in which you play as the legendary Dragon of Dojima), you'll come across glowing yellow circles, marked on your mini-map as blue book icons. Interact with seventy of these, and you'll unlock this. There are 50 Memoirs to be found in the various regions of Ijincho, Yokohama, and 40 Memoirs located across Kamurocho. That means you only need to nab a portion of the 90 Memoirs, but, not only is it nice to reminisce as Kiryu, but each one builds his Soul (Brawler), Tech (Rush), and Body (Beast) stats, so they're worth collecting. Some are also substories, and they're almost always worthwhile, too.