The following contains spoilers for Dr. Stone: Ryusui, streaming now on Crunchyroll.
Created as a bridge between Season 2 and Season 3, the new special Dr. Stone: Ryusui adds a lot of new technology to Senku’s arsenal. Not only is he planning to sail to the other side of the planet, he and his crew establish a supply of cloth and even take to the sky for the first time. But all of this is small in comparison to the biggest gear in the machine of modern society: money.
Born into an ultrarich family, Ryusui has never wanted for anything and only acts in his own interest. His place in modern society also means that he knows the game of money as well as he knows the ways of the sea. He effortlessly proposes the boat runs on oil, as it’s the best fuel that modern man had for any vehicle. While Senku had planned the same thing, Ryusui takes it a step farther. He demands the rights to any oil field that the group finds, and creates his own currency so that those rights have weight. Single-handedly, Ryusui restarted capitalism in the stone world, with all of its pros and cons.
Up to this point in Dr. Stone, Senku has depended on bartering and trade to get what he needs. He needed to win the Great Bout to get access to alcohol and Ishigami Village, and he needed to promise that his inventions were helpful before others helped him. Eventually, everyone realized that helping Senku meant enjoying the spoils of his creations, be it furnaces providing warmth in the winter or a bowl of ramen.
This system works just as well as money, but it requires more effort. First, the exchange of goods and services has to be done in a way that each party involved gains something. For example, if someone’s skills don’t match what Senku needs, they would be of no value to him at that time. If compensation isn’t the issue, then those assisting him need to want the outcome too, like how Nikki insists that she just wants to help in the special. However, if one party can't give the other something they want, the deal would fall apart.
As money is reintroduced, the exchange of goods and services has become easier. All anyone has to do to get something they want is have enough drago to pay for it. Senku and the gang start selling food and clothes to meet this goal, starting a new economy in the process. A successful currency allows everyone to contribute, even just a little.
With the benefits of this system, though, come the drawbacks. The first and most notable is greed. People will always try to hoard resources, and money is one of the easiest. Those who have money run the world, and the characters from the modern time know this very well. It doesn't take Yo long to start schmoozing, or for Ryusui to spend his money in excess because he can.
Of course, no system is perfect. Regardless of the rules, people will always find a way to exploit it for their own benefit. Senku, Gen and others do this all the time in Dr. Stone. While firmly set in the idea that humanity and all its creations are good things, the series also points out the problems. Like in the battle with Tsukasa, who was against rebuilding modern society, where neither ideology comes from an evil place.
Money is the most influential concept in the world. It's responsible for creating and breaking bonds between countless people, and the cause of plenty of wars. It lets the world function, but is also the cause of a lot of its problems. If nothing else, Dr. Stone: Ryusui is a simple, concentrated example of its pros and cons.