There is an image of this cultivar on the Hosta Library. From the photo on the HL website, it appears to be a miniature to small size hosta with dark green leaves and narrow, creamy white marginal variegation. It is a form of H. kikutii var. polyneuron. This non-registered cultivar was originated in the Wakayama area of Japan. 

Mikiko Lockwood in an article on The Hosta Library titled, A Little About Japanese Hosta Terms defines the term shirofukurin or shiro fukurin as white-edge(d) or white-margin(ed) and the term yama as mountain.