Miracle Warriors: Seal of the Dark Lord, known as Haja no Fūin (覇邪の封印, lit. Seal of the Dark Lord) in Japan, is a role-playing video game released initially on the Japanese PC-88 and then ported to various other systems, including a Sega Master System version which was released in North America. It's somewhat similar to Phantasy Star in gameplay. The game came with an elaborate grid-format map noting areas of interest in the game.

Each screen consists of four parts. In the lower left are all character statistics. It lists all characters in the party. Each character has a life bar and experience bar. A single character can gain experience by hitting enemies. Once the experiences is full, a new level is reached. The experience bar is emptied and both bars are extended, resulting in more maximum life for the character and more experience needed to gain a new level. On the lower right are statistics for the entire party (for example the amount of money). The upper right section varies from screen to screen. While traveling the world, a town or a maze, a map is shown where the player can navigate. If the player invokes the main menu, it will be shown there. In battle it shows the battle menu. The upper left section also varies. While traveling the world or a cave it shows the party members and their surroundings. In battle it shows the foe and in town it shows persons to which the player can talk and their dialogue.

The world is built in grid-format. The player can move around. On the world map and towns the players location on the map is marked by a white square. Once the player encounters an enemy, the screen switches to battle mode. The player can choose one character to attack per turn. This character will also be subjected to the attack of the enemy, unless the enemy uses a spell that attacks multiple players. Some enemies can use flame spells to attack all party members or sleep spells that can put multiple party members to sleep. Every time a party member is put to sleep they take damage. They can wake up and be put to sleep many times during a battle, taking damage each time they fall asleep again. Once every party member is sleeping, the enemy will use a flame spell to attack every party member at once. As an alternative to attack, a player has several options, including talking, retreating, using a magical item, or casting a spell. Some enemies respond to talking and give hints.

The currency in the game is the guilder which can be used to buy items or heal the players. Defeated enemies also yield fangs, which are proof of valor in battle. Fangs can be used to buy some exclusive items or traded in villages for guilders.

Defeating enemies can also increase or decrease the player's character points (fame). Killing monsters usually increases the player's fame while killing good characters (for example merchants) decreases the player's fame. A certain amount of character points is required to enter certain villages.