This game features 3 main protagonists in their fight against evil female assassins known as Black Sheep. The title is probably supposed to be "Night Sheep" but the spelling is consistantly wrong, so I'll leave it as is. Each level is a board, where the heroines battle enemies, losing clothes and stripping opponents. Defeating an opponent then nets jigsaw puzzle piece which is used to graduate to the next level.
There is a brief review (in Japanese) of this game on the ADVGAMER blog