An article by
George Schmid in
Hosta Journal (1996 Vol. 27 No. 2) states that this
is an "old" incorrect name for Hosta
longissima longifolia 'Nakafu Nagaba Mizu'.
Mikiko Lockwood in an article on The Hosta Library titled,
A Little About Japanese Hosta Terms defines the term nakafu as medio-variegated, the term nagaba as narrow long leaf(ed).
and the term mizu as water or 'Mizu Gibōshi' which is the Japanese name for the species
are at least 3 hostas with this Japanese name but they are each of a different species as follows:
H. kiyosumiensis 'Nakafu' and
longissima var. longifolia 'Nakafu'.