Jonathan Sizemore is a character from the anime Gunslinger Stratos: The Animation, originating from the Square Enix arcade game of the same name. In the story, he is associated with the operations of a specific administrative district, known as Ward 17. His primary function within this setting is as a member of the Engineering Department, where his duties largely involve performing maintenance and upgrades for his own mech, a type of combat unit called a PUG.

Sizemore is defined by his role as a frontline combatant who pilots the PUG, a machine designed for close-quarters combat. The PUG is built with a focus on getting close to opponents, prioritizing both weapons power and durability. Its standard equipment includes a pair of Wrecking Arms, which are wrecking balls attached to energy tethers. These are effective at short range for destroying enemy obstructions and shields but only have a single shot. For additional firepower, the PUG is equipped with an automatic shotgun on its right arm, which offers wide frontal coverage, and an automatic beam cannon that serves as a heavy weapon, though it requires a brief moment to charge before firing. For melee combat, Sizemore uses Blade Arms, which are powerful and have a wide attack range but are somewhat slow to deploy compared to other melee weapons.

In the narrative of the anime, Jonathan Sizemore is one of several characters who meet their end fighting against a formidable antagonistic force known as the Dead End. His fate is shared with other characters in the series, marking him as a participant in the dangerous conflict that defines the story's climax.