WARNING: The following contains spoilers for BLEACH: Thousand-Year Blood War, Episode 2, "Peace From Shadows", now streaming on Hulu and Disney+.
In the second episode of BLEACH: Thousand-Year Blood War Part 2, two battles between Shinigami Captains and Quincy Sternritters take the spotlight as Yhwach's forces advance upon the Seireitei unannounced, yet again. During her battle against Sternritter K, the robotic BG9, Soi-Fon was confident due to her mastery of a technique that she hadn't quite gotten the hang of in her last encounter.
Invented by the genius Yoruichi Shihōin, the Shunkō technique is a devastating trump card that was once used to subdue Soi-Fon herself. What is the Shunkō technique, and is it something that is powerful enough to replace a plundered Bankai? Here's the explanation of Soi-Fon's new trump card.
Origins
As mentioned before, the Shunkō is not new to the BLEACH universe, as it was first introduced by Soi-Fon during her fight against her former master Yoruichi Shihōin during the Soul Society arc. Soi-Fon's hubris was particularly evident in that battle as she'd believed herself to be the inventor of the technique; however, it had actually already been perfected by Yoruichi – the inventor of the Shunkō technique. It is a high-level Kido manipulation technique that combines hand-to-hand combat with the spell-based Kido. As such, it combines two of the cardinal elements of Shinigami combat: Hakuda – hand-to-hand combat; and Kidō – "Demon Arts". As Captains of the Onmitsukidō (Covert Ops) branch of the Gotei 13, both Soi-Fon and Yoruichi are extremely proficient at the aforementioned hand-to-hand combat. To perform the technique, its user would drive huge amounts of Reiatsu into their arms and legs, which grants them huge boosts in speed and strength while also manifesting as wind (or lightning in the case of Yoruichi).
During their fight in Soul Society in early BLEACH, Soi-Fon claimed to not have a name for the technique; however, Yoruichi revealed her knowledge and mastery of it, telling her former disciple what she named it. She also revealed that the reason for the lack of sleeves on their uniforms was because the fabric would be torn away upon the technique's activation. The word "Shunkō" is written 瞬閧 in Japanese, with the first kanji "Shun" correlating with "an instant" or "instantaneous"; however, the kanji contains radicals that mean "eye", "dance" which also align it with "blink". "The blink of an eye" is a famously short period of time and so this first kanji carries with it literal and symbolic conceptions of instant, while the "-kō" kanji in "Shunkō" translates to "battlecry", so together the Shunko technique is named for the swift movement and booming sounds related to its attacks landing. The sheer spectacle of the technique as it is used also communicates a preparedness for battle.
Back to Basics
Soi-Fon and Hitsugaya's respective battles are shown together in the second episode of BLEACH: Thousand-Year Blood War Part 2 for the reason that both Captains have had to go back to the drawing board after having had their Bankai plundered in the previous cours. For Hitsugaya, that meant relying more on his lieutenant, Matsumoto, and learning to get used to having less destructive force than he once did. For Soi Fon, losing Jakuhō Raikōben meant brushing up on the basic tenets of her style of combat, resulting in the incredibly powerful Shunkō she developed for her rematch against BG9.
The tenet of Shunkō that Soi-Fon masters prior to her rematch is something she discovered after her fight against Yoruichi: Mukyū Shunkō ("Infinite Shunkō"), a technique that makes the reiatsu she emits whirl around her indefinitely, maintaining the technique for as long as she wills. As the technique's name suggests, Soi-Fon's movements were instantaneous, and she was able to close huge distances between herself and her mechanical opponent very quickly. The sheer impact of her attacks was explosive given her speed; however, the robot was able to quickly assimilate data of Soi-Fon's newfound strength into its memory banks and even that swiftness that made it look like she had a chance was quickly and easily matched by the Quincy.
Yoruichi's Shunkō
As mentioned earlier, the technique manifests in either wind or lightning, with the latter being associated with Yoruichi's application. What is yet to be revealed in the anime; however, is Yoruichi's own furthering of the concept as seen with Soi-Fon's Mukyū Shunkō. Beyond the basic concept, Yoruichi takes Shunkō multiple steps further as her reiatsu manifests in different ways while maintaining the flowing, zapping electricity. In one application called Shunkō: Raijin Senkei ("Thunder God Battle Form"), lightning from Yoruichi's Shunkō takes on the form of the drums of Raijin (or Raiden), the thunder god from Japanese mythology. Yoruichi then unleashes a powerful column of electricity that overwhelms the enemy. Yoruichi also has a final trump card beyond this next step of Shunkō; however, that exciting development will only come in later episodes of this final arc.