There is an image of this
cultivar on the
Hosta Library. From the photo on the HL website, it appears to be a
size hosta with slim, lanceolate, green leaves and
yellowish-green medial (center) variegation. There seems
to be some red dots at the base of the petioles. The
pale bluish lavender flowers bloom in September followed
by viable seeds. This non-registered
cultivar was originated in Japan and is considered a
sport of H. 'Tortifrons'.
Mikiko Lockwood in an article on The Hosta Library titled,
A Little About Japanese Hosta Terms defines the term nakafu as medio-variegated.