Under the bonnet, HKS has retained the standard car's 1.6-litre turbocharged three-cylinder petrol engine, which in Toyota-tuned factory guise develops a respectable 200kW of power and 370Nm of torque.
However, the tuner has fitted a larger turbocharger – running nearly double the standard car's boost pressure, at nearly 40psi – plus a new intercooler, revised ECU tuning and a 100-shot of nitrous oxide.
The result? A staggering 349kW of power – an increase of nearly 75 per cent over the production model's figure.
It's mated to the standard GR Yaris's six-speed manual transmission and variable all-wheel-drive system.
Complementing the power boost is a full Rocket Bunny widebody kit, comprising wide wheel-arch flares, a deep front splitter and larger side skirts. A large rear wing sits attached to the tailgate, while Craft Square-branded mirrors adorn the doors.
Filling the arches are 18-inch Advan Racing R6 wheels wrapped in sticky Yokohama tyres. They hide HKS-designed coilover suspension at all four corners, matched with the standard GR Yaris's high-performance brakes.
Bride carbon-fibre race bucket seats and a MoTeC race instrument display headline the changes inside the cabin.
While the liveried show car you see here won't enter production (or be sold to the public) in its current form, a range of parts fitted to the vehicle will be offered as aftermarket add-ons at a later date through HKS importers and retailers around the globe.
For a closer look at the HKS GR Yaris's powertrain and visual upgrades, click here to read Speedhunters' in-depth tour of the car at the tuner's Japanese HQ.