How do you earn Heroes of Mavia?

How do you actually acquire the Heroes of Mavia in the game? Are there specific missions or quests that players need to complete to unlock these heroes? Or is there a chance element involved, such as random drops or loot boxes? Also, is there a way to increase the chances of obtaining a rare or powerful hero? Understanding the mechanics behind earning Heroes of Mavia will help players strategize and optimize their gameplay experience.