This sword technique demands a high level of explosive power from the legs, hence the "Lightning Flash" is indeed the most rudimentary form of the Thunder Breathing, yet it is also the most difficult to master among the six main forms of the technique.
So, if one were to channel their power into one leg while using the Sun Breathing as with the Thunder Breathing and then release it in a burst to execute a high-speed assault, what would that become?
The answer, Reiger had just demonstrated it.
Tearing through the air was no longer the sound of thunder, but a deafening blast.
The flash was no longer that of lighting, but of fire.
The strike delivered wasn't the "Lightning Flash," but a "Round Dance."
This was an extension technique of Sun Breathing used once by Kamado Tanjirou in the original 'Demon Slayer' series— the "Round Dance Flash."
When Reiger was pondering how to increase his speed while using Sun Breathing, he suddenly remembered this move's existence.
