A Japanese game developing studio.
From Japanese Wikipedia http://ja.wikipedia.org/wiki/トーセ:
With license connections to many game companies, Tose boasts over 1000 titles released for different platforms and mobile phones, and is regarded as the biggest secondary company on the game market.
However, as Tose never claims any copyright, and only displays the original copyright owner on their games, it's impossible to track a complete list of their works. They are therefore knows as "she shadow warriors" of the game world.