In the years from 1945 to 1955, the Kobayashi group made a steady and continuous rise to the top of the wholesale pharmaceuticals field in Japan.

The superstition that an Osaka wholesaler advancing into Tokyo would surely fail was knocked to pieces. Tokyo Kobayashi Daiyakubo, which started business with just five people, grew to over 150 employees before the end of 1955. Taking advantage of their central location they expanded beyond the traditional household medications, to carry many more products that helped maintain stable business operations.

On the other hand, the Osaka headquarters was steadily expanding its business scope, and continuing to develop the branch offices established after the War in Kobe, Kyoto and Hiroshima. Many young employees, overflowing with enthusiasm, gathered around Saburo, often rising through the ranks to shop manager or agent, even in their 20's.

The environment surrounding Kobayashi Daiyakubo was also steadily getting brighter. With the post-war confusion fading from the Japanese economy, and inflation that had swept furiously through the country finally starting to settle, steady footsteps toward recovery began to echo across the land. In particular, the start of the Korean War in June, 1950 brought a boom in special procurements for the Japanese economy. This laid the groundwork for the "Golden Age" of the Japanese economy in the 1960's.

Upon this backdrop, the Kobayashi Group continued to fortify its greatly expanded base through the whole period. In April 1954, seven years after moving into Tokyo with Tokyo Kobayashi Daiyakubo, the Osaka headquarters merged with the Tokyo subsidiary to form a single business. Tokyo office became a branch office of Kobayashi Daiyakubo. With a seven-year business record Tokyo's "Osaka Allergy", which was a concern when first entering the Tokyo market, was clearly not a worry, and there was no longer a need to operate separately. Furthermore, by merging, better economies of scale could be exploited for business conditions promising even more efficient operations.

In June, 1955, the Tokyo branch moved from the Chiyoda ward to Nihonbashi Honcho.

With this move, the shop floor space increased dramatically, but more importantly, it established a Kobayashi presence in the stronghold of Tokyo's Medical and Pharmaceutical Industry, akin to Doshomachi in Osaka. The office was surrounded by new pharmaceutical manufacturers and other companies in the field, yielding many intangible benefits to Kobayashi Daiyakubo.