Tsukuyomi, a malevolent cosmic entity, rules from his mobile space station, Death Star Yomi, located on a comet. His primary objective is reviving the destructive eight-headed dragon Yamata no Orochi by collecting eight sealed orbs scattered across the planets of the Onam System, analogous to Earth's solar system. Before the main events, he destroyed seven planets to acquire their orbs but failed to secure the final orb sealed within Ismo due to the rebellion and subsequent disappearance of his most powerful bio-mechanical weapon, Susanoo, for millions of years.

During the ancient conflict called the "time of the gods," Tsukuyomi waged war against divine forces. Following his defeat, Orochi was sealed into eight capsules, one buried in the core of each planet. Tsukuyomi later initiated a campaign to retrieve these capsules, destroying each planet in the process and reducing the Onam System to the single surviving world, Ismo.

Tsukuyomi's presence induces catastrophic natural phenomena: devastating seas, hurricane-force winds, volcanic eruptions, and lightning blasts that ignite forests. These effects intensify as he approaches planetary bodies. His powers encompass energy projection, teleportation, creation of structures like armor or lunar temples, summoning meteors, and telepathic communication across interstellar distances. He alters celestial mechanics, such as causing a permanent solar eclipse by shifting the Moon's orbit.

After millennia, Tsukuyomi returns to the Onam System to secure the last Orochi orb. He dispatches bio-mechanical warriors called Sky Soldiers to retrieve Susanoo, now bonded to a human child named Yamato Takeru. Tsukuyomi's forces repeatedly attack Ismo to eliminate Yamato and reclaim Susanoo.

Reclaiming the Sword of Dark Clouds—a weapon housing a significant portion of his power originally extracted by Susanoo from Orochi—restores Tsukuyomi to full strength. This enables him to trigger worldwide geological disasters and manifest Orochi's form: an eight-headed dragon capable of space travel, breathing crimson lightning and fire.

In the *After War* OVA, Tsukuyomi resurfaces when a fragment of his Dark Sky Carriage crashes near Yamato's village. Employing a parasitic strategy, he latches onto Oto Tachibana's mother to absorb Oto herself, using her as a hostage and power source. This forces a confrontation where Yamato pilots Susanoo to intercept Tsukuyomi heading toward the sun. Tsukuyomi is ultimately destroyed when Mikazuchi sacrifices himself by piloting Susanoo into the sun, annihilating both.

Tsukuyomi's essence exhibits cyclical resilience; his defeat by Susanoo in ancient times and later sealing by the gods did not permanently eradicate him. Post-*After War*, implications suggest his eventual return in a less malevolent form.