At first, I thought the butterfly on my photo was the Lesser Grass Blue (Zizina otis).
However, that species has blue-brownish eyes and not black eyes.
The Holly Blue (Celastrina argiolus) also looks quite similar to Sugitani's Hedge Blue (Celastrina sugitanii) which also has black eyes and occurs in Japan.
However, the latter flies in early spring, from March to May and usually lives only for two months.

Kanazawa, Ishikawa Prefecture, Japan, 25 September 2018