High Grenadier is a turn-based strategy game with role-playing elements. The game has a rather abstract plot that depicts a battle between two human organizations, each piloting and commanding giant mechs; no further details are revealed in the game. The gameplay takes place on a battlefield composed out of dots connected by lines; both player-controlled and opponent's army can move only between adjacent dots.

The player has six commanders at his disposal; each of them can lead a several various mechas into the battle. Three commanders are available initially, while others can be called into battle later. Once a player-controlled and an enemy unit meet on the same dot, the player can order the commander to attack, defend, or retreat. The battle then proceeds automatically, its result calculated by the statistics of both units. The role-playing element involves leveling up mecha parts; a number of experience points is awarded after a battle, and the player can freely distribute them to raise the mecha's parameters.