This is a non-registered
longissima longifolia from Japan. It is a medium
size hosta about 14 inches tall. The pale lavender
flowers with purple stripes bloom in August.
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