To provide a cooperative play control method, a storage medium, and a game device urging the characters in a friendly team to participate in a cooperative play at a battle against an enemy and allowing them to feel a solidarity feeling in the team.

One life point value common to individual characters in a friendly team is calculated. When the physical strength level value of one of the characters becomes 0 after the start of the battle against a hostile team, 1 is subtracted from the life point value, and the physical strength level value of this character is reset to the value immediately before the start of the battle. When the life point value becomes 0, all players in the friendly team are made game over. When the physical strength value of the boss character of the enemy becomes 0 before the life point value becomes 0, a bonus is given to all characters.