Sideways first appeared as a beam of light from the sky striking a large Earth city near the Autobot base. An enigmatic warrior, he appeared to side with the Autobots, helping Hot Shot by watching his back during a confrontation with Scavenger. When asked to reveal himself, he transformed, his rider quickly splitting and becoming a helmet that covered his entire head. He claimed to be Sideways, a drifter who just wandered into the conflict. While he gave the human kids Billy and Fred rides in cycle mode to keep them entertained, Hot Shot and Red Alert as well as Rad and Alexis were suspicious of the motorcycle's motives, especially his close attention to the Mini-Cons.
In the following battle, Megatron faced Sideways and Hot Shot alone, and managed to force the Mini-Con panel Sideways had (apparently) found out of his grasp. As the Decepticon leader began to warp away, both Autobots grabbed onto Megatron and all three were teleported to the Moon. To Hot Shot and Megatron's surprise, the Mini-Con panel was a fake, made to convince Megatron to retreat so that Hot Shot, spurred on by Sideways's encouragement, could defeat the Decepticons once and for all. Though both robots fought well alongside each other, with Sideways expressing concern over Hot Shot's well-being, he eventually betrayed the young Autobot, by striking a deal with Megatron. He would pretend to be Megatron's hostage and in exchange, no matter what, Hot Shot would turn over the Star Saber. At first, Hot Shot did follow through, but reneged at the last moment by calling the Mini-Cons back to him. Sideways suddenly attacked Hot Shot, knocking the Star Saber out of his hands and kicking it to Starscream. He switched Mini-Con heads, revealing his allegiance to the Decepticons. Hot Shot was savagely beaten by the Decepticons, who stopped short of destroying him on the advice of Scavenger, who teleported the young 'bot back to the Autobot base. Once Sideways's loyalty to the Decepticons seemed to be confirmed, he began manipulating them and playing them against each other to suit his mysterious goals.
Sideways watched with indifference as the Decepticons became divided over Starscream's possession of the Star Saber. Even though Demolisher turned to him for support, Sideways claimed that he wasn't one for "taking sides". On the next Mini-Con hunt, Sideways crossed paths with Hot Shot, though he avoided fighting him. Instead he took on taunting the young Autobot (who gave chase to him). Hot Shot managed to knock him off his wheels on their second of such races, which allowed the Autobot to regain some confidence in himself.
When Starscream voiced his concerns that Scavenger went to joining the Autobots after deserting the Decepticons, Sideways stood in agreement with him. He put on a front of being especially spiteful towards Scavenger. stating that no one should get away with betraying the Deceptions. Starscream was right and thanks to Scavenger's superior tactics, Megatron was gravely injured and tossed down a crevasse on the Decepticons next mission. Sideways hauled him out, but with the Decepticon leader too damaged to continue fighting, the Decepticons were forced to retreat.
Megatron decided to take out his frustration on his troops, and had them participating in a "training excercise", where he chased them around with the Star Saber, Sideways tried to sit the whole thing out, only for Megatron to find his hiding place and dedicate all of his efforts on chasing Sideways specifically.
With Sideways help, the Decepticons nearly secured the Mini-Con Incinerator (losing hi to the Autobots at the last moment, due to Blurr's arrival) and then went after the last memberof the Skyboom Shield trio, Downshift. This Mini-Con was somehow able to activate on his own, and fled from anyone who approached him. As one of the speedier Decepticons, Sideways gave chase to Downshit, only to be blasted by Smokescreen and taken out of the race.
One of these goals was the replacement of Megatron as Decepticon leader after a series of significant losses. Sideways sowed the seeds of rebellion within the Decepticon ranks, subtly turning Starscream against Megatron and convincing Megatron of Starscream's imminent treachery. The situation came to a head when the two Decepticons fought outside their base, but Sideways then realized Megatron would never execute Starscream for his insubordination, exposing an ever-constant weakness within the Decepticon command structure. After the battle, Sideways mused that this weakness would come back to haunt Megatron one day, and would be his ruin. Fortunately though, this incident somehow served to solidify the Decepticons as a unit, giving them much greater morale and cohesiveness, and achieving Sideways's aims of giving neither faction in the conflict a clear advantage.
Shortly thereafter, Sideways tried to hack the Autobot base computer, only to encounter the children attempting to destroy the equipment to stop Sideways. He transported them to a digital universe, where they saw the coming of two new combatants. He tried to threaten them into handing over the Street Action Mini-Con Team, before the kids realized that as this wasn't real, he could not harm them. Sideways then apologized to an unseen master, shortly before the children escaped the digital universe, chased by an unknown entity.
The Decepticons began to distrust Sideways, suspecting he was not what he seemed, and realized he was manipulating everybody in the unit. Caught out by Thrust and the other Decepticons while communicating with his unseen master, Sideways panicked and attempted to escape, but not before he was confronted by Megatron and sliced in half with the Star Saber. Sideways simply reformed each time, reconnecting his parts and absorbing laser blasts from the other Decepticons. Megatron, in fury and disgust, hacked Sideways to pieces and he was seemingly destroyed... or so they thought. Sideways had entered trans-phase mode and his rider rose in the form of a twisted nanite creature before the Decepticons' eyes, declaring that the Star Saber and Skyboom shield were merely toys to him, as he was near-invincible. His rider said there were millions of Mini-Cons left to be found, and challenged Megatron to see who would find them first, before flying off to parts unknown.
While most of the Autobots were on Earth fighting the monstrous new Decepticon recruit, Tidal Wave, Sideways made an appearance inside the Autobots' base... on a monitor! He told Red Alert and Alexis about the Requiem Blaster, and how the Autobots must find the three Mini-Cons that form it before the Decepticons do. Neither of them trusted Sideways, but they knew Sideways was right. If the Decepticons did find the Requiem Blaster first, it could spell doom for the Autobots and the galaxy.
Awakening Once the Autobots had acquired the Requiem Blaster, Sideways appeared once again on the Autobots' monitors, laughing. He showed them that he'd disabled their defenses. Sure enough, the Decepticons infiltrated the Autobot base, took the Requiem Blaster, and nearly killed Smokescreen in the process.
Later, Sideways appeared to the Decepticon tactician, Thrust, and told him that the Requiem Blaster would be even more powerful if used in conjunction with the other two Mini-Con weapons, the sword and the shield.
Thrust talked with Sideways again in a secret, ominous meeting. They planned to get the Mini-Con weapons away from the Autobots.
Thanks to Starscream's confusion on where his loyalties lay, he was able to steal the other two weapons from the Autobots, giving the Decepticons all three weapons. Thrust was hard at work on a secret project for Megatron, one that would harness the energy of all three weapons, and Sideways congratulated the tactician on his growing duplicity. When the three weapons were combined to power the starship Hydra Cannon, Megatron used it to blow up a nearby comet while Sideways laughed from afar, on Earth's moon.
Both the Autobots and Decepticons were en route to Cybertron when a few of each faction were warped to a strange planet where they fought a dark copy of Optimus Prime called Nemesis Prime. When Optimus Prime and Megatron combined their firepower against it, Nemesis Prime was destroyed, and as the copy dissipated, Sideways appeared momentarily. Nemesis Prime had merely been Sideways' puppet.
When both sides had arrived on Cybertron, a black hole opened up over the planet. It started becoming apparent to some that Unicron was arriving. An apparition of Sideways appeared over the Autobots, and the Mini-Cons attacked it. After telling the Mini-Cons to get lost, Sideways again disappeared. Sideways returned to swear vengeance against the Mini-Cons when they tried to stop the black hole's effects.
Eventually, Thrust became suspicious that his partnership with Sideways and Unicron might be found out, so he panicked and stole the Requiem Blaster and Skyboom Shield. Thrust ran deep underground where he met up with Sideways, but he was tailed by Starscream. Starscream declined Sideways's obligatory offer to join Unicron, and the two fought. Sideways assaulted Starscream with strange tendrils and amoeba-like organisms, and he and Thrust were able to leave with the two weapons. Now inside the moon in Cybertron's orbit, Sideways placed the Mini-Con weapons into its core, revealing that the moon was Unicron lying dormant all along.
The last of the three Mini-Con weapons was dropped by Starscream when he sacrificed himself to Unicron to prove to Galvatron (a transformed Megatron) that Autobots and Decepticons must join forces to destroy Unicron. Sideways formed over what was left of Starscream and grabbed the sword, making an easy getaway.
With all three weapons in place within Unicron's core, Sideways's master was able to shed the rest of his moon disguise and show his real form. Sideways and his patsy Thrust celebrated their inevitable victory over time and space.
Thrust was told by Sideways to leave, as his work for now Unicron was now done. Thrust was confused, thinking he would be Unicron's right-hand man, but Sideways got angry, and ordered him to leave immediately. Thrust, dejected, left for the surface, where he briefly dictated himself into opposing Sideways so he can assume his command as Unicron's trustee. However, this was not meant to be when he later got crushed to death within Unicron's creases during the battle.
Optimus and Galvatron managed to reach the glowing core deep within Unicron's body. Before their eyes, the core budded, recreating the body of Sideways. Unicron spoke through this Sideways body, announcing that Sideways had always been an extension of Unicron himself, and that Sideways had intentionally stoked the flames of the Autobot/Decepticon war so that Unicron could be fueled by their mutual hatred. He took special delight in mocking Optimus Prime for claiming to fight a war for peace, a seeming contradiction. The truth, according to Unicron/Sideways, was that Optimus Prime loved to battle; Prime refused to admit this. Unicron/Sideways wrapped Prime and Megatron in tendrils, drained Galvatron of his energy, and offered Prime the opportunity to merge with him. Then the children and their Mini-Cons arrived, and they pleaded with him to stop, but Unicron/Sideways was able to claim them as their own; the Mini-Cons were Unicron's creation, after all. But inside a dreamworld created by Unicron, the children were able to call out to the Mini-Cons. They reactivated and told Unicron/Sideways that they believed in peace, and would fight for it if necessary. Their combined might was able to help Prime break free of his tendrils before Prime receives his powerlinx colors. Enraged by the Mini-Con's retaliation, Sideways lashed out in an attempt to kill Hire-Wire, but Optimus quickly shot a blast through Sideways using the Requiem Blaster. As what was left of Sideways faded, he claimed he'd have his revenge before passing away. Immediately after this, Optimus and Galvatron begun their final confrontation.