The player begins at the lowest rank in the Garden, number 255. The object of the game is to destroy Perfect1, who is ranked number 1. After eliminating a rithm, the player may then absorb its energy by walking through the cloud of static it leaves behind. Doing so gives a boost to one of three statistics: maximum defense (hit points), maximum offense (ammunition) or maximum agility (fuel). The tougher the opponent defeated, the larger the boost that the player receives. The weakest are the "Goners", who are all ranked number 256, and therefore yield no increase in rank when destroyed, even at the beginning of the game. Picassos, Torks, Kilroys, Venuses, and Davids are more powerful than Goners, and each individual among them has a unique rank."
"Movement is akin to that of a combat flight simulator, though restricted to the ground. Pressing up on the D-pad causes the player character to accelerate, which consumes agility. Once in motion, the player rithm will continue moving forward at the same speed until it accelerates further, runs into an obstacle, or comes to an immediate stop (accomplished by pressing both shoulder buttons simultaneously). Though running into an obstacle prevents the character from advancing, its legs continue to run, and if turned away from the obstacle the character will resume moving at the same speed as before. If the player character runs out of agility, movement is reduced to a slow limping. Agility can be replenished by standing still or visiting the DOAsys, a small neutral zone where the player character can converse with other rithms, including boss characters. Offense and defense can be replenished at the recovery spires found throughout Perfect, or at the DOAsys. Other rithms also use recovery spires, and their resources are finite. However, they are regularly recharged during "storms". Standing on a recovery spire during a storm drains the player rithm's defense."
"When a player’s rithm is destroyed, it receives a decrease to its stats, and the player character is sent back to the “real world.” The player character may also voluntarily jack out from Perfect at any of the recovery spires, or at the DOAsys. While in the real world, the player may review the net gains (or losses) to the player character's stats since the last jacking out, view statistics on their performance, save the game, or load a saved game. A game over is only reached if the character's Defense stat reaches 0, or if the character loses the final boss fight."
"In order to confront Perfect1, the player must first defeat the other ten bosses. Unlike other enemies, bosses generally do not wander through Perfect, and can be confronted at their specific lair at any time the player chooses. However, boss lairs disappear during storms, leaving the bosses to wander freely until the storm ends."
Released in Japan under the name Perfect World.
Source: Wikipedia, "Immercenary", available under the CC-BY-SA License.