Void reincarnated into Void Termina. The ancients sent the four heroes of yore (which included Galacta Knight) to defeat him. The heroes of yore sealed Void Termina away, the ancients then feared Galacta Knight so they sealed him away and the science ancients banished the magic ancients (which included Hyness) away because they knew that they were too OP. So Hyness got angry and tried to released Void Termina to get his revenge on humanity. Thousands of years later, he succeeds, but Kirby has killed literal gods in the past so he has no problem with defeating Void Termina. Then Void's negative emotions disappear and he will now come back as a friend in the next game (or later than that).