Ultraman Mebius Gaiden: Ghost Rebirth

Ultraman Mebius returns to his usual position in "Nebula M78". On the planet Ultra, Sophie sees Ultra Sign asking for help from "Ultra". Man Hikari" who is close to "Monster Graveyard" where no one is likely to live. So Sophie ordered "Ultraman Taro" and "Ultraman Ace" to advance there. and ordered Mebius to advance to the tomb first. But what Mebius found was Golzam who was probably dead. The Taro's found Mephilus and Deathrem, members of the "Dark Gods Four" who were probably dead. Why did they come back? And what about Hikari, who hasn't been found yet? Or is this the prelude to a new war for the Ultra Warriors?