The Gatotsu (牙突) is a form of Hirazuki, which is a technique designed by the second in command of the Shinsengumi, Hijikata Toshizō. According to dialogue in the Ruroken series, the Gatotsu is Saitō's invention, created to maximize destructive power whilst minimizing the user's exposure to strikes. However, due to the fact that the user runs straight ahead to perform a thrust with his left arm, there is a small blind spot that leaves the right side of his body exposed while the move is being performed. There are four variants of this move.
- Gatotsu Isshiki (牙突壱式): This is the standard, shoulder-level ground attack. The user prepares by dropping into a partial crouch, both knees bent, left arm drawn back and right arm extended forward; he grasps the kashira (endcap of the tsuka, or hilt) of his sword with his left hand and rests the tips of the fingers of his right hand (usually the thumb) on the blade near the kisaki (blade's tip).
- There is also an overhead version of Isshiki which Saitō called "the true form of the Gatotsu". It is possible that this is a stronger and faster version of the Gatotsu since Saitō stated that he was no longer holding back when he used it on Kenshin.
- Gatotsu Nishiki (牙突弐式): The user adopts a position similar to the one seen in Isshiki; however, his arms are positioned slightly differently, with the blade pointing diagonally down. The attack itself is not a lunge, but a jump followed by a downward thrust as the user is landing. Also, the direction of the Nishiki thrust is narrower than in Isshiki.
- Gatotsu Sanshiki (牙突参式): The user adopts a position similar to the one seen in Isshiki; however, his arms are positioned slightly differently, with the blade pointing diagonally up. The attack itself is not a lunge, but a hop in conjunction with a thrust.
- Gatotsu Zeroshiki (牙突零式): A point-blank range Gatotsu that requires no prior preparation or footwork. Instead, the user tenses and utilizes all of the power in his upper body, bringing both arms backward and then thrusting with the one holding the katana to pierce anything in the sword's path. Saitō in particular has shown to be strong enough to pierce through thick solid materials, be it Usui's tinbe shield or Yatsume's arm.