This is a sport of H. longissima longifolia from Japan. It has strap-like foliage that is green with a gold colored medial (center) variegation.

According to The Hostapedia by Mark Zilis (2009), "This name is not a recognized botanical name and should not be used. The specimens I've observed do not differ from 'Asahi Star' or H. longissima 'Kinakafu Nagaba Mizu'."

Mikiko Lockwood in an article on The Hosta Library titled, A Little About Japanese Hosta Terms defines the term kinakafu or ki nakifu as yellow-center(ed), the term nagaba as narrow long leaf(ed). and the term mizu as water, 'Mizu Gibōshi' or H. longissima.