Quintet was a game company closely affiliated with Enix, and seems to have become defunct in 2002. They're responsible for many older games in addition to the ActRaiser series, most notably, perhaps, the Soul Blazer trilogy (Soul Blazer, Illusion of Gaia, and Terranigma). In fact, those familiar with early Quintet games will recognize many of the sound effects used (Soul Blazer's "damage" noise is the same as the Master swinging his sword, for example).