The TD-MK4 is what happens when a defense contractor builds a sparring robot. Tessera Dynamics designed it for military close-quarters combat training, and it shows. The machine is built on a military-grade chassis with ballistic armor panels visible under thin padding, moves with the speed and precision of Tessera's combat automata, and fights with a controlled violence that makes users genuinely afraid. This is the point. Fear inoculation is the primary training objective — teaching soldiers and operators to think and fight while their hindbrain is screaming at them to run.

The MK4 operates in training tiers from Level 1 (compliant drilling partner) to Level 8 (lethal engagement simulation). Levels 1 through 5 are standard military issue. Level 6 requires unit commander authorization. Level 7 requires medical staff on site. Level 8 has resulted in deaths and is technically restricted to 'unmanned facility testing,' though rumors persist of black-site programs that run operators through Level 8 scenarios. The machine at Level 8 uses actual combat techniques at near-full speed with force limiters barely engaged. It is, at that point, a combat automaton pretending to be a training aid.

Tessera sells the MK4 exclusively to military and corporate security clients, but units enter the secondary market regularly — stolen, lost in logistics, or quietly sold by corrupt quartermasters. These units end up in underground fighting venues, where promoters pay premium rates for a machine that can genuinely hurt people. The underground fighting scene around MK4 units is a significant and growing subculture, with fighters earning substantial purses for surviving rounds against an increasingly unlocked Opponent.