What is mienai?

Some articles on mienai:

Mienai Chikara (Invisible One)/Move
... "Mienai Chikara ~Invisible One~ / Move" is the nineteenth single and first Double A-side by B'z, released on March 6, 1996 ... "Mienai Chikara ~Invisible One~" was used as the first ending theme of anime series Hell Teacher Nūbē ...
Mienai Hoshi
... "Mienai Hoshi" (見えない星 Invisible Star) is Mika Nakashima's 21st single ... "Mienai Hoshi" is used as the theme song of the dorama Haken no Hinkaku ...
Yūko Ishibashi - Discography - Video Game Contributions
... SOUND TRACK~STARRY WORLD~(May 25, 2006) 見えないチカラ / Mienai Chikara (credited as YOU-CO ...