According to my speculation, in the quest of "Heroes: The Last Blade", the Sphere of Eternity might have been obtained from a well hidden below the center of the Eternal Fortress. Of course, this is just my guess. I can explore it in the game. If you are interested in the Invincible Heroes series of games, I recommend the novel "Invincible Heroes in Online Games". It tells the story of the protagonist who was reborn into the Invincible Heroes 3 and 5 games, bringing with him the knowledge of his previous life, becoming an expert in the game, and realizing his dream of playing the game. I hope you like this fairy's recommendation. Muah ~😗