Nova Co., Ltd. is a contract developer that worked closely with a lot of publishers during the 8-bit and 16-bit console eras. In particular, they helped develop a lot of Namco games for the home market, as well as develop the games of toy giants Bandai, Tomy and Takara. They are thought to be linked to Sun L, which also created many similar games with Bandai and Takara. Both Sun L and Nova Co. Ltd. created a lot of games in Bandai/Banpresto's Compati Hero Series franchise.
More infromation: Nova Co., Ltd.'s GDRI (Game Developer Research Institute) page. Nova Co., Ltd.'s GameFAQs page.