A possible explanation for why Akaza's Air Type changes from blue to red is that the color represents the increase in the physical intensity of the attack.

Akaza's Air Type functions by creating shockwaves through his strikes. When he punches or kicks, the force generated compresses the air in front of him which is what creates the high-pressure wave that travels toward his opponent. At lower levels of output, this compressed air remains stable so it's blue.

But when Akaza increases the speed and force behind his attacks, his strikes would apply a much greater amount of mechanical work to the surrounding air, and so, the molecules are forced to be closed together in an extremely short period of time. Because the energy has little time to escape, the compressed air would rapidly increase in temperature through a process similar to **adiabatic compression**, which is a process where a gas is compressed so quickly that it does not have enough time to transfer heat away to its surroundings. Instead, the energy used to compress the gas increases the movement of the molecules themselves, which causes the temperature of the gas to rise rapidly.

In Akaza’s case, the faster and more powerful his strikes become, the more pressure is applied to the air in front of his attacks. Because this compression happens almost instantly, the air cannot release the added energy quickly enough, which causes it to become extremely hot. As the temperature rises high enough, the compressed air could begin to emit visible light through **thermal incandescence**, which is the same principle behind objects glowing red or orange when they become extremely hot, such as heated metals or the air surrounding objects moving at extreme speeds through an atmosphere.

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Under this interpretation, the red is because the physical conditions of the attack have changed, it becomes shockwaves that has reached a higher threshold of velocity, pressure, and energy density so that the surrounding air itself becomes superheated.

So Akaza's basically pushing the physics of his BDA.

(Reminder that it's just a theory, probably not the reality)

A theory on why Akaza's BDA turned red