A sword-roaring battou. Still wielding two swords, she takes a firm stance and:
Lesser Celestial Thrust… then after overpowering the opponent with her swords’ energy to damage their spirit;
Greater Celestial Phenomenon… Musashi lets out her final blow with all her might.
The Niou appearing behind her is just a side-effect of her swords’ pressure.
It can be considered an embodiment of the sword of “Zero”, the concept of “Void” Musashi has yet to master.
It’s called an Anti-Unit Noble Phantasm, but it is actually an Anti-Fate Noble Phantasm.
A Buddha sword that wards off all forms of untimely deaths, karmic damage, curses and tragedies in a single sweep.
“After you scraped off something’s existence to the extreme, to the point you could say it no longer has any, “something” still remains.”
The extreme “One” they say “no two of” can be found.
The “Zero” that is beyond it… the concept of “ ”.

The Flower of Tengen keeps striving to reach this throne.

When she draws her sword for the Greater Celestial Phenomenon, she mentions Tenman Dai-Jizai Tenjin’s name. The historical Musashi Miyamoto was a devout of Tenman Dai-Jizai Tenjin, and he can be considered his guardian deity.
Tenman Dai-Jizai Tenjin is the name given to the heavenly god of the Dazai Prefecture’s Tenmanguu Shrine; in other words, the amalgamation of the thunder god and Japan’s most prominent vengeful spirit Sugawara-no-Michizane and Dai-Jizai Ten Mahesvara (also known as Shiva, the Hindu God of Destruction).
Additionally, Dai-Jizai Ten is also considered an avatar of Guanyin.
In reality, before Sugawara-no-Michizane started to be worshipped as the heavenly god of scholarship at the end of the Heian Era, he had already been conferred the divine name of Tenman Dai-Jizai Tenjin, so, putting it bluntly, Tenman Dai-Jizai Tenjin is Sugawara-no-Michizane’s aspect as a wrathful god traced over to Shiva.
It is speculated that the reason Musashi chose the thunder god as the object of his devotion is because most kenjutsu practitioners before him and their schools were devout to the Kashima Shrine, and the god Takemizuchi worshipped there was said to be the thunder god’s ancestor.
Takemizuchi, the god of thunder-turned-god of kenjutsu.
In response to that, since Musashi chose to perfect himself on “the art of the sword” instead of “the technique of the sword”, he did not devote himself to the same god of thunder or kenjutsu, but to Tenman Dai-Jizai Tenjin, who also has an aspect as the god of scholarship. Or so it is speculated.
Additionally, at the time (and even now), Dai-Jizai Ten was often confused with Ishana Ten, the king of a place named Take-Jizai Ten, due to their similar names.
Ishana Ten is considered to be on the same god as Izanagi, the ancestor god of Japan. And, due to how its name is pronounced, he is associated with Shana-ou (Minamoto no Yoshitsune). Since Yoshitsune was, even at the time, considered the originator of the samurais’ militarization, Ishana is implied to be connected to both Japan and the origin of samurais.