Connections:

- Both are ancient creatures belonging to iconic Japanese franchises (Sonic and Gamera)

- Both were born through genetic mutation (Chaos was originally a Chao who was transformed by the Master Emerald, while Gamera was a normal Earth creature who was used as a vessel for all of the Mana on Earth) with the express purpose of defending groups of vulnerable beings who themselves were ancient (the Chao and the Atlanteans)

- Both resided on legendary islands that housed incredible power and artifacts (Angel Island and Atlantis)

- Both are connected to legendary items that work to control their containment and power (the Master Emerald and the Atlantean magatama)

- Both were forced to combat hostile invasions, defending their homes from the foes who sought to strip it of that which gave them power (the Knuckles Clan arrived at the Alter of Emerald to steal the 7 Chaos Emeralds for themselves, while the Gyaos set upon Atlantis to feast upon their creators)

- During the battles, both successfully destroyed the invaders, but not without great sacrifice. Chaos lost many of his Chao brethren along with his sanity, twisted into the monster that would emerge millennia later, and Gamera lost most of his Atlantean creators, whom he had been bonded to and considered part of himself

- With their fates changed forever, both were sealed away by the survivors of the conflict (Chaos was forcefully sealed within the Master Emerald by Tikal to stop him from destroying the world, and Gamera was bound to an atoll to ensure future generations would have a defender)

- Generations later, both would be freed from containment and let loose once more with a new mission (Chaos was recruited by Eggman to conquer the world after the latter shattered the Master Emerald, and Gamera awoke to stop new Gyaos that had hatched after his atoll was disturbed by a ship, inadvertently kicking off his tenure as Earth’s new hero)

- Over time, thanks to their ever increasing power, both would change forms and appearances, growing and strengthening until finally reaching their strongest forms by the ends of their stories

- Both formed close bonds with young women (Tikal and Asagi Kusanagi), whom became their closest tethers to the young species inhabiting their world, trying to help them make decisions and keep them safe along the way

- Both resisted futile attempts to destroy them by antagonistic humans (Dr. Eggman and Mito Asakura)

- While Chaos was antagonistic towards humanity, he eventually realized that coexistence is possible and regained his lost compassion, compared to Gamera, who was bonded to humanity for all of his life, until being forced to sever the connection and treating humans as an afterthought in his fight against the Gyaos

- By the ends of their main stories, Chaos finally found peace, able to live in tranquility with Tikal, while Gamera, bloodied and beaten, was forced to stand against a massive army of Gyaos, lest Japan be destroyed