Necros no Yōsai is based on the characters from the eponymous Japanese toy line from the 1980s. The story tells of a world known as Tankirie, which was conquered by the evil warlock Necros; however, eight heroes (Knight, Mage, Amazon, Samurai, Elf, Dwarf, Berserker, and Mercenary) defeated him and restored peace. The game is divided into chapters; in the first one, the player takes control of the Mercenary, who is separated from his companions and is looking for a job. A search for a girl's missing father leads him to more dangerous discoveries, and eventually he has to reunite with his friends in order to face the evil once again.
The player controls the Mercenary in the first chapter, but plays as other heroes as well (up to an active party of three) later in the game. The game is structured like a traditional top-down Japanese-style RPG, with random enemies and turn-based combat viewed from first-person perspective. Stand-out feature of the game are animated attacks: every attack in battle is presented as a short animated sequence, separate from the battle screen.
Unlike most other RPGs of the time, Necros no Yōsai does not feature a freely explorable "world map". Instead, player-controlled characters move in a strictly linear fashion to icons that represent towns and hostile areas.