Eternal Poison takes gamers into a beautiful strategy RPG set against the backdrop of a dark medieval fantasy kingdom. The story begins with the mysterious abduction of Princess Valdia by the demonic kingdom of Besek, which demands the coveted Eternal Poison as ransom. As gamers progress through this dark and twisted storyline, they are faced with five different stories, each unfolding through the eyes of a different main character. These different perspectives are woven together to reveal the secrets and dangers that lurk within the kingdom. The heart of Eternal Poison is a turn-based combat system that takes place on grid maps, offering gamers a strategic battlefield.

Controlling six characters, users engage in battles where tactical skill is of paramount importance. The characters have different skills and magic, which makes the gameplay more difficult. A unique feature of the game is the ability to capture and summon demons – the very enemies that inhabit the unforgiving landscape of Besek. These demons, once under the player's control, can become invaluable allies in the fight. It is noteworthy that demons serve several purposes at once. Users can use them in battles, sacrifice them for valuable items, or extract mana from them to enhance their own abilities. The dynamic and multi-faceted role of demons brings an intriguing layer of strategy to the game, forcing gamers to make important decisions that resonate throughout the gameplay.