Shigure Soen Ryu (時雨蒼燕流, Shigure Sōen Ryū?, lit. "Shower in Late Autumn, Blue Swallow Style") is a dynamic sword art that increases incrementally as it is passed from master to student. It is also called as the "Invincible Sword Style". Shigure Soen Ryu is used by three people in the series — Takeshi Yamamoto, Tsuyoshi Yamamoto, and Superbi Squalo. The Shigure Kintoki is a special sword used by Takeshi in conjunction with the Shigure Soen Ryu.
The Shigure Soen Ryu originated from one man. Like a family tree, the technique grew as it was passed down. It is a tradition for a generation to add a new form to the Shigure Soen. This is a sword style that varies, depending on who your master was. Thus, there could be many different variations of the Shigure Soen Ryu.
The Shigure Soen Style is a notoriously deadly sword style that is only passed down to worthy successors. Each form of the style is only shown once to the student - if the student is worthy to succeed, he only needs to see it once to remember how to use it from then on. It originally only had one form that was passed down through generations of successors with each successor creating and adding their own forms resulting in many branches of Shigure Soen Ryu. However, as new forms were created, the weaker branches deteriorate, and others disappear as there is no worthy successor; hence, this style can be called the perfect, flawless style.
- 1st form: Shajiku no Ame – Offensive. Takeshi charges forward and attacks with a thrust.
- 2nd form: Sakamaku Ame – Defensive. Takeshi obscures his body with a wall of water, while at the same time defending it with a contraction.
- 3rd form: Yarazu no Ame – Offensive. Takeshi drops the katana, kicking it with his foot, to send it flying in a stab.
- 4th form: Gofuu Juuu – Defensive. Takeshi synchronizes with his opponent's breathing to evade attacks.
- 5th form: Samidare – Offensive. Takeshi does a slicing attack while switching the katana between the swing, changing the trajectory and the timing freely..
- 6th form: Unknown, deducted to be defensive.
- 7th form: Shibuki Ame – Defensive. Takeshi holds the sword backwards and spins to create a whirlwind like shield.
- 8th form: Shinotsuku Ame – Offensive. Takeshi uses the blade of the sword to cut around the bearer. Takeshi can also use Rain Flames with this move if there's no water. An alternative version was used by Future Takeshi with hot water called Shinotsuku Nettou.
- 9th form: Utsushi Ame – Offensive. Takeshi makes a tidal wave with his sword and, while his opponent is distracted by his reflection, he attacks from above.
- 10th form: Scontro di Rondine – Offensive. A tidal wave of Rain Flames surrounds him while he charges, led by the Swallow from his Box.
- 11th form: Beccata di Rondine – Offensive. Takeshi thrusts his blade multiple times with one hand.
- 12th form: Sadachi: Kirisame – Offensive. Takeshi uses the Jirou left sword of his Cambio Forma Version Vongola Gear to attack with multiple compressed airwaves which can "Sniff" out an enemy, making this perfect against illusionists.
- 12th form: Udachi: Kirisame – After Sadachi: Kirisame, this attack is different in that the waves are shaped like Kojirou and can cut the opponent who has been "sniffed" by Jirou.
- Aggregate Art: Jiunoka – Defensive + Offensive. Takeshi combines all his forms to strike moving objects with rain flames, causing them to slow down to the point that they appear to be frozen in place.
- An alternative 8th form, Autumn Rain, was created by Tsuyoshi's fellow apprentice.
- Both the 10th and 11th forms have a strong resemblance to Squalo's Zanna di Squalo and Scontro di Squalo. It is possible Takeshi used these attacks while developing his own forms.
- Future Takeshi could perform many of Squalo's techniques, and while the present Takeshi has not been seen directly using the techniques, he has been seen using them within Shigure Soen. For example, when he strikes Genkishi with a form, he unleashes Attacco di Squalo at the same time.
- Takeshi's two forms for the 12th form, which involve using the left blade and right blade separately, are both very similar to Genkishi's Danza Spettro Spada.