SCR-HD was a robot produced by MeteorTech who appeared in Sonic Riders: Zero Gravity, and essentially the main antagonist of the game. It contained an Ark of the Cosmos until it spontaneously exploded, and was taken by Storm. SCR-HD was the leader of the more common, mass-produced SCR-GP and used its own Ark of the Cosmos, as well as the one in Eggman's master computer, to command all the MeteoTech robots.
SCR-HD was originally a simple robot created by Dr. Eggman's MeteorTech company, presumably in the MeteorTech Sparkworks, and was controlled by Eggman's mother computer in the Crimson Tower. While appearing harmless and a part of a security company's products, the purpose of SCR-HD and the rest of its robot bretheren was to be sold to various other organizations around the world and become an integrated function of society, for then, on Eggman's orders, to go on a rampage and seize control of the different regions in Eggman's stead, so the doctor could complete his Eggmanland project.
During the beginning of Sonic Riders: Zero Gravity, however, one of the Arks of the Cosmos crashed into the storage facility where SCR robots were stored in stand-by mode. Due to Eggman having the control unit of the Ark of the Cosmos as the core of MeteorTech mother computer, the program inside the Arks of the Cosmos took control of the SCR robots, SCR-HD included, and compelled them to gather the five existing Arks of the Cosmos with the purpose of bringing them back to Babylon Garden. SCR-HD itself, took possession of the Ark of the Cosmos that triggered the rampaged and became the out-of-control SCR robots' leader. Using the world's SCR robots, SCR-HD ordered its robots brothers to collect the Arks of the Cosmos located across the world.
SCR-HD was first encountered by Sonic, Tails and Knuckles while they were making their way to Megalo Station. It, as well as several SCR-GP, pursued Sonic and co. until they fell from a window. While falling, Sonic unintentionally activated his Ark of the Cosmos and was saved from the fall. SCR-HD, as well as six SCR-GP raced Sonic through Megalo Station and were defeated.
It appeared again in the Security Corridor where it broke in after the race and stole all 5 Arks of the Cosmos from Wave. It then flew away to the Babylon Garden, which was transformed into Astral Babylon by the 5 Arks. SCR-HD then transformed into Master Core: ABIS, and battled everyone on the Mobius Strip. It was defeated and disappeared into a black hole, where it was presumably destroyed.
SCR-HD is unlockable in Sonic Riders: Zero Gravity by beating it in Free Race Mode. Like SCR-GP, it doesn't ride an Extreme Gear and simply curls itself into a wheel as it were a Gear itself. In gameplay, SCR-HD is a Fly Type character. It functions as the only permanent Air Ride-type Gear with no Gear Parts. Just like the rest of the playable characters in the game, SCR-HD can perform Gravity Control and Gravity Dive using the Ark of the Cosmos he has stored internally in its body.
- Because only one SCR-HD is seen in the story, it is unknown if it is mass produced like the SCR-GP.
- SCR-HD is vaguely reminiscent of Neo Metal Sonic in that it is a robot that got away with mass scale theft to fulfill a higher goal (although SCR-HD seems to be merely a pawn to the Arks of the Cosmos compared to Metal's bloodthirsty motives), and ultimately transformed into a monstrous, all powerful flying creature rooted to a large object (Metal Overlord to a tower, Master Core: ABIS to the black hole's core.)
- Just like his weaker counterparts, SCR-HD has what appears to be a sword, specifically a katana, that he pulls out when he obtains the "attack" power-up. However, SCR-HD holds it differently.
- Like his weaker counterparts, SCR-HD has many similarities to the Droideka from the Star Wars series.
- SCR-HD and SCR-GP are the only Sonic Riders characters who don't need an Extreme Gear, as they can curl up into a ball.