Isekai⇔Chikyuu-kan de Kojin Boueki Shite Mita

Wataru discovers a portal connecting Japan to a fantasy world. Observing the underdeveloped society there, he identifies opportunities to profit by importing items like sugar, spices, coffee, and hygiene products. He earns significant wealth by selling these goods. Later, after seeing a potion for sale, he decides to bring healing potions to Earth, which are highly valuable. He also purchases slaves from the other world and achieves success in Japan as well.