Sideways serves as a covert operative for the planet-devouring entity Unicron, though his precise origins remain deliberately obscured. Some accounts suggest direct creation by Unicron as an extension of the entity's will. Alternatively, conflicting narratives propose he originated as a survivor of Planet X, destroyed millennia ago in a catastrophic war against Gigantion, subsequently entering Unicron's service seeking vengeance. Sideways himself actively propagates contradictory stories about his past, embracing the ambiguity.

He transforms into a purple and yellow racing motorcycle. His defining characteristic involves two Mini-Cons, Rook and Crosswise, who combine into a single entity named Mirror. Mirror acts as his rider in vehicle mode and transforms into interchangeable heads for his robot mode. Switching between these heads allows him to display either Autobot or Decepticon insignia, facilitating infiltration of both factions. His combat capabilities include arm-mounted cannons or blades. He possesses unique abilities derived from Unicron, such as entering a "trans-phase" state where he becomes intangible, immune to conventional weapons like the Star Saber or Skyboom Shield, and capable of instantly reforming after sustaining severe damage, even dismemberment. He can also interface with technology, hacking systems and manifesting within digital spaces or computer monitors.

His core motivation revolves around serving Unicron's goal of consuming Cybertron and other worlds. To achieve this, he manipulates the conflict between the Autobots and Decepticons, ensuring neither side gains a decisive advantage, thereby prolonging the war and generating the hatred and chaos that nourishes and revives his master. He demonstrates no loyalty to either faction, dismissing their conflict as trivial and their labels as "petty." He exhibits a distinct pleasure in betrayal, particularly savoring the shock and despair of those he deceives.

Within the *Armada* narrative, his actions begin with arrival on Earth via a beam of light near the Autobot base. He initially presents himself as a neutral drifter named Sideways, joining the Autobots while using the Rook head to display their insignia. He gains their tentative trust, interacts with human children, and secretly observes the Mini-Cons. During a mission to the moon with Hot Shot, he orchestrates a trap for Megatron using a fake Mini-Con panel. After fighting alongside Hot Shot, he betrays the young Autobot, striking a deal with Megatron, attacking Hot Shot, delivering the Star Saber to Starscream, and switching to the Crosswise head to reveal Decepticon allegiance.

Operating as a Decepticon, he continues manipulating events. He subtly fuels the rivalry between Megatron and Starscream, aiming to replace Megatron as leader, but ultimately exploits Megatron's refusal to execute Starscream to solidify Decepticon unity, maintaining the stalemate. He sabotages potential Decepticon victories, feigning defeat and covertly attacking Cyclonus during a decisive battle to allow Autobot reinforcements to secure the Skyboom Shield. He also attempts to hack the Autobot base, trapping human children in a digital realm to extort Mini-Cons, though he fails when they realize his digital form cannot harm them; this incident forces him to apologize to Unicron.

His true nature is eventually exposed to the Decepticons by Thrust. Cornered while communicating with Unicron, he faces attack. Megatron slices him apart with the Star Saber, but Sideways repeatedly reforms and absorbs their energy blasts. After being hacked to pieces, he reveals his trans-phase ability, his body dissolving into static as Mirror rises as a nanite creature. He declares the Decepticon weapons useless against him, challenges Megatron to find the remaining Mini-Cons, and departs.

Operating covertly post-exposure, he continues manipulating both factions. He contacts the Autobots to warn them about the Requiem Blaster and disable their base defenses, leading to the Decepticons stealing the weapon. Simultaneously, he corrupts the Decepticon Thrust, convincing him to gather the three legendary Mini-Con weapons (Star Saber, Skyboom Shield, Requiem Blaster) to revive Unicron. When Unicron awakens and attacks Cybertron, Sideways, revealed as Unicron's puppet or avatar, confronts Optimus Prime and Megatron within Unicron. He traps them, but after they escape with human help, Unicron sends Sideways to stop them. Optimus Prime ultimately destroys Sideways using the Requiem Blaster within Unicron's core, a crucial step towards Unicron's defeat.

Despite apparent destruction, Sideways resurfaces two decades later during the events of *Cybertron*, sustained by Unicron's lingering dark power, though initially lacking memories of his past service due to the Unicron Singularity. His personality shifts dramatically; he becomes more laid-back, frequently listening to and singing music, and forms a friendship with Soundwave. He resumes his role as a faction-switching agent, eventually joining Starscream's splinter group. He regains his memories and reveals his origin as a survivor of Planet X alongside Soundwave, seeking revenge against Gigantion. He now pursues the Cyber Planet Keys and the Omega Lock for this vengeance, no longer serving Unicron directly. His story concludes when he and Soundwave attempt to seize the Omega Lock during a battle between Starscream and Galvatron on Gigantion. The resulting energy surge blasts Sideways, Soundwave, and Starscream into another dimension. Later glimpses show Sideways and Soundwave on a restored Planet X within that alternate dimension.

In other continuities, such as the Dreamwave *Armada* comics, his role is less defined. He is seen working with Decepticons on a secret rocket project on Earth and later appears among the Cybertronians during Unicron's arrival, showing fear like the others, lacking the cartoon's depiction as a dedicated Unicron agent. The *Revenge of the Fallen* film features a separate character named Sideways, a cowardly Decepticon courier with no connection to the Unicron Trilogy character.