During promotional profile shots of the Ultra Warriors in the series, Tregear Early Style is portrayed copying Taro and Taiga's pre-fighting stances. Prior to his fall, Tregear used to look up on Taro as his Only Friend who excels in fighting. Even if Tregear is a Non-Action Guy, deep down, he admires Taro and it even influences on his fighting prowess.
In episode 7, Tartarus attacked Planet U40 (Joneus and Titas' home planet) after recognizing the danger it would bring to his plans in the future. As revealed in The☆Ultraman, Planet U40 was once invaded and taken over by the Heller Empire, forcing its inhabitants to be purged out of their Planet and the final series itself is to retake it from Heller's possession. Tartarus' endgame is pretty much a retread of Heller's only his involve a hostage crisis (using Yullian) instead of a full force planetary invasion. Since the people of Planet U40 had first hand experience of being invaded and forced out of their homes, Tartarus predicted that its people would aid the Land of Light Ultras should he ever started to invade the Land of Light too.
After the end of The Absolute Conspiracy, it made sense as to why Zero quickly departed from Earth instead of joining Z's fight on Earth and Haruki leaving Earth by joining with Z. Yullian is still under captivity, which is still a major crisis in the Land of Light. Zero was required to return in order to rejoin the frontlines in saving Yullian again, while Z does the same, now that he has Delta Rise Claw and Beliarok as his aide. Not to mention, any Ultras that appeared on Earth to assist Z up until his departure were all under the factors of attracting them to Earth; Geed appeared because of Gillvalis and Greeza, Zero appeared because he was incapacitated mid-way, only to leave once assuring that Z can handle things himself and Ace appeared because Z's Medal signaled him when Baraba was rampaging.
In addition, Genegarg's simple theft of Hikari's Ultra Medals and Z Riser is pretty much explained here that a) the Ultras were too occupied with Tartarus' campaign and b) most of the elite Ultras were off-world either to combat Tartarus, the Devil Splinters and/or in the Ultra Brothers' case, severely weakened because they had to fight Parallel Isotopes of Juda, Mold, Belial and Tregear. Coupling all these lead to their planet having little defenses and securities that allow Celebro to steal said items and setting forth the motion of Ultraman Z.
Fridge Horror
Tartarus' original plan is to evolve a Maga-Orochi into Magatano-Orochi. Way back in its first appearance in Ultraman Orb, the Planet Eater's evolved form was so powerful, that its Achilles' Heel resulted from an Imperfect Ritual in the mid series was the only way out, and Orb and Juggler were lucky for their opponent to have such weaknesses. The Maga-Orochi in Planet Mikarito would likely evolve into the Magatano-Orochi without such weaknesses, as well as the fact that Gudis Cells used to empower it came from Gudis, a monster that is actually so dangerous that in its home series Ultraman: Towards the Future, Great acknowledged it as an intergalactic level threat which required a number of the Land of Light Ultras to interfere.
Creating Parallel Isotopes like Juda, Mold, Belial and Tregear didn't actually affected the main timeline itself, but Tartarus did so and thus any timeline he interfered, according to Zero, has become diverged. This opens up a universe where Ultraman Geed was never conceived because Belial was out of the timeline and another where the Taiga Spark never finished its construction.
Alien Bat is resurrected sometime after the events of Ultraman Saga which ends with Dyna, Cosmos, and Zero (along with the Ultra Brothers in the director’s cut) leaving that version of Earth. With no one to stop him, it’s entirely likely that Alien Bat took his revenge on that Earth, or at least used it as testing grounds for Zett.
