In 1890, at the age of 16, Kametaro, the first son of Kinjiro, succeeded him in the family business. Two years preceding this transition, Kametaro started helping his father in the business and came to know their customers. Kametaro was very studious and in addition to working in the family business, he attended Tokyo Commercial College (Hitotsubashi University). Although most merchants' sons of those days ordinarily found jobs after graduating from senior courses of the primary schools, Kametaro was an exception. He was so eager to learn, and his father Kinjiro had foresight.

Maruiya was, however, burned to the ground in the great fire of 1899. In his dedication to restore the family business, Kametaro was unable to continue with college. It took him seven years to finish with his studies and to graduate. After graduation, he worked for Naigai Trading and Iwasaki Copper Trading House, also running the family business. He learned trading during this period. However, his busy schedule did not keep him from hobbies which he enjoyed, such as judo, boating, tennis and horseback riding. Like his father, Kametaro was a man of few words with a determined spirit.

An opportunity came to Kametaro who was anxious to restore his family business. Rising Sun Company offered him a petroleum transportation business. The newly-born Rising Sun was established by Samuel Company, known today as Showa Shell Sekiyu. At the time Kametaro became involved in the handling of petroleum, tin containers were used. Damage to the containers during discharge from the ships was a common problem. Kametaro then looked into this problem and he reduced damage drastically by distancing the tin containers from ships' structures and by placing experienced personnel in key positions. With this accomplishment, Kametaro gained the confidence of Rising Sun.

In 1909, a petroleum storage terminal was built in Fukagawa, Tokyo. From this storage point, petroleum was to be distributed to Tokyo by tank wagons. Kametaro acquired three tank wagons of his own and entered the business of land petroleum transportation.