Era of Defense is a first person open world game, in which your character is stuck back in time with a powerless time machine, surrounded by prehistoric people and prehistoric dangers. You must collect crystals from various sources to power up your time machine and travel back to the present. Crystals are given as rewards for quests given to you by locals, in which you defend sacred temples from onslaughts of enemies. Gain experience points through battle, which you can exchange for ever better weaponry, such as more advanced axes, hammers and bows, which in turn allow you to fight more difficult enemies.