Kumagusu’s research was accelerated when he returned to Japan. Shortly after his return, he focused on collecting aquatic specimens, but after moving to Nachi the lives in the forest became his main target.
In addition to this, he immersed himself in writing and publishing essays in Nature, Notes and Queries, or Science. This was also the period during which he conceived of the idea of “Minakata Mandala” in correspondence to Dogi Hōryū. He met Koaze Shirō, who would later be his important research collaborator, in the same period.
During his Nachi days, Kumagusu’s interest gradually shifted to slime molds, which was to be the focal point of his research for life.
After he settled permanently in the town of Tanabe, he collected fungi and plants from around Tanabe and continued his research from home.