When IDW's 2005 Transformers line of books began, main architect Simon Furman consciously chose to ignore the traditional Primus and Unicron mythology that he himself had created while penning the original Marvel Transformers comic, mainly due to the concurrent Unicron Trilogy of cartoons featuring the two deities predominantly. Following Furman's removal however, various authors would occasionally reference Primus but merely as a religious belief. Unicron was never even referred to by name, only being known as the "opposite" of Primus.
The proper build-up began in issue #34 of Robots in Disguise which saw the introduction of IDW's Thirteen Primes and served as a stepping stone for more traditional Cybertronian mythology into IDW's universe. Issue #10 of Optimus Prime would later speak of the ancient Titans doing battle with Primus's "opposite", with Unicron making his first physical appearance on the final page of First Strike two months later.
Unicron picks up in the immediate aftermath of "The Falling"; following the events of Joe Colton's invasion of Cybertron and the subsequent clash between Iacon and New Prysmos, the mysterious Talisman has successfully awoken Unicron, who begins an attack on the galaxy by devouring the Cybertronian colonies scattered throughout the galaxy. This monstrous attack has been orchestrated by "Onyx Prime"—now revealed as Shockwave—in a gambit centuries in the making; by unleashing Unicron to destroy Cybertronian civilization, Shockwave reasons, he can then rebuild Cybertronian society anew on Earth.
Optimus Prime leads a force to Rom's homeworld of Elonia to try and evacuate the planet, discovering that each world has been targeted by Shockwave's old Regenesis project as part of his time-travelling exploits as Onyx Prime. Though Elonia is safely evacuated, the planet is not so lucky and is unceremoniously swallowed by Unicron. A subsequent attempt at stopping Unicron over the planet Caminus sees Prime and a small group of allies unsuccessfully try to destroy the monster from within, though they discover an ancient relic in the process: a ruined Omega Sentinel robot. On returning to Cybertron, Bumblebee links with Omega Supreme to learn the full story behind Unicron's creation: eons ago, during the reign of the Thirteen Primes, "Onyx Prime" and his retinue led a colonization mission to the planet Antilla, the first planet to be colonized by the Cybertronian race. The native species fought back against Cybertron's imperialism, and a desperate scientist created a doomsday weapon designed to wreak ultimate vengeance upon Cybertron: the Talisman itself, the device twisting the fabric of reality to create Unicron and the monstrous Dire Wraiths.
This respite is short-lived, however; having devoured twelve of the colonies, Unicron—now merged with the Titan Nemesis—approaches Cybertron in his new robot mode, intent on finishing the planet. Having double-crossed Starscream's "Decepticon Vengeance Division", Shockwave's lackey Bludgeon leads the evil Decepticons and the bestial Maximals into an orbital dogfight over Cybertron, successfully destroying Carcer and Elita One with it. Though the Cybertronians fight their hardest, they are unable to prevent Unicron from beginning his attack on their homeworld.
Salvation comes from an unexpected source: the Spectral Knights of New Prysmos are capable of using their own magic to activate the Talisman, projecting a beam of energy which teleports the population of Iacon to Earth, with Blurr sacrificing himself to save as many people as possible before Unicron rips the planet in half.
Regrouping on Earth, Shockwave begins his final plan to transform Toronto into the capital of his "New Cybertron", believing that Unicron was felled by the Talisman when the Decepticon scientist tricked it into eating Cybertron. Little does he suspect that his plan has failed, and that Unciron now approaches Earth supported by Bludgeon and the Maximals, having turned on their former master for manipulating them over millennia.
Elsewhere on Earth, heroes and villains unite as Unicron's approach causes havoc, and as the Maximals descend on Earth to find and destroy the Talisman Optimus hatches a risky plan, recruiting Arcee and the three Seekers for a mission to activate the Talisman in the heart of Unicron and destroy the monster from within. Events culminate in a massive battle for Earth as heroes and villains from across the Hasbro Universe join forces to repel the Maximal invasion, and as the battle reaches its zenith Starscream sacrifices himself to bring the Talisman online.
Within the black hole heart of Unicron, Optimus is forced to make the ultimate sacrifice, willingly throwing himself into infraspace in the hopes of bringing Unicron down from within. Bolstered by Soundwave's own suicide play, tapping into the afterlife to bolster Optimus with the souls of the departed, Optimus relies on their faith in him as he confronts the vengeful specter of Unicron's creator, eventually convincing the alien to let go of his hurt and move on. Renouncing his title as Prime, recognizing that the title was flawed from the start, the alien and Orion Pax die together, collapsing Unicron into a new black hole and ending the threat for good.
In the aftermath, the characters take stock of their victory; Shockwave is arrested by Prowl and brought into custody, Slide learns to let go of her anger at the Prime, Pyra Magna steps up to lead the Cybertronian refugees on Earth, and the Cybertronian species, freed from their dark past at last, settle into life on their new homeworld: Earth.
The series is penned by John Barber with lineart by Alex Milne, and colors by Sebastian Cheng and David García Cruz. Sara Pitre-Durocher, Andrew Griffith, and Kei Zama provided art in addition to Milne for the series's double-size final issue, which also featured coloring by Joana Lafuente. Six connecting B-covers were done by Transformers veteran James Raiz.
- This series was originally solicited as Transformers: Unicron: The Darkest Hour.
- Contains issues #1 to #6.
- Bonus material CURRENTLY UNKNOWN