Based on the anime series, this is an action/rpg developed by Westone who also developed the Monster World series. The battle scenes in particular will be instantly recognisable to Monster World fans as they have very similar art and gameplay styles.

In this game you travel the world trying to save Wataru from the evil antagonist Darkdar. The main overworld display is the standard top down view of most JRPG's, complete with random battles. Once you engage your enemy the perspective switches to a side view where you pilot your mech and battle against monsters. It's fast and fluid and all played out in real time, with jump and attack mapped to your A & B buttons.