The sudden lore bomb. So, during the period where Demon King is in hibernation while Mars went through the terraforming, humanity seems to have developed genetic modification that allows human to protect themselves with Mana in place of spacesuit. The first of them is sent to Mars, but even he found the terraforming work will be challenging. When hearing human had started making the next generation of the Martian, he had his worries. He see himself as not so different from human, outside his ability to slightly better to survive space. But the next generation is more powerful, and he worried they will start seeing themselves as above humanity, which lead to war. He jokingly nicknamed them Mazoku, short of Mars Zoku, but also a call out to the demon race's name.