Long time ago, the Gods fought the Demons in a cosmic battle. To ensure victory, the Gods had to sacrifice part of their divine nature, and forge a weapon that had both good and bad in it - the "Evil Holy Sword" Necromancer. The demons were forced to dwell in the lower world, while the Gods remained in the heaven. Between these two worlds lies the world of humans. But the demons did not accept this plan for co-existence. They have murdered the king of the human continent Ishumeria, and it's time for the nameless hero of this story to seek out the legendary sword Necromancer, and restore balance in the world.
Jaseiken Necromancer plays like a traditional Japanese-style role-playing game: top-down navigation, linear story progression, turn-based battles against randomly appearing enemies, automatic leveling up, etc. A somewhat unusual (for the time) feature is the player's ability to choose two companions for the hero among six possible ones. These warriors are introduced to the hero after he accepts his quest, and the player can build a party of three, trying to balance between physical and magical skills they possess.
The game is also notable for its rather dark themes, uncommon for the representatives of its genre at that time. Enemies mostly include demonic creatures, and their death animation contains graphical gore.