It's just a theory but i'm guessing this was tg-16 answer to ninja gaiden on the nes.   While the decades have past and ninja gaiden has moved on to bigger and better things, poor ninja spirits has been stored in the dusty drawer of videogame history.  i'll be honest does the game play hold up today???  no but for some reason i still keep coming back for more.  i love the power up system and the extra selection of weapons made the game that much more fun to play.