Engetsuzan

Engetsuzan, also referred to as Shunpō , is 's and Bankai Ichigo's side special move in Super Smash Flash 2.

Overview
When performed by Ichigo, he holds his sword back and then quickly dashes a far distance straight forward to perform a slash in front of him. The move can be charged for a short period of time, with the move traveling farther and dealing more slash damage and knockback the more the move is charged: 8% with no charge and 10% with a full charge. When dashing forward, he uses a technique called "Flash Step" in which he completely disappears until the slash at the end to create the illusion of teleportation, and an afterimage of himself is created where the move is used. Ichigo is completely invincible in this state and opponents hit are dealt the same amount of damage and knockback as they would be from the slash.

Because of the speed and invincibility Ichigo has while dashing, the move is useful for maneuvering around the stage and dodging attacks. However, it also suffers from some startup and ending lag, making it easier to punish and vulnerable to certain lingering attacks. The far distance it travels makes it a useful horizontal recovery tool, though it also leaves Ichigo helpless at the end.

Yami Shunpō
Bankai Ichigo's version of the attack is called Yami Shunpō. This version of the move is slightly faster and does not leave Bankai Ichigo helpless when used, but it travels a much shorter distance and cannot be charged. The move deals 12% slash damage and more knockback than Ichigo's counterpart, and it has much less startup and ending lag. Additionally, when used in midair, the move can be cancelled into almost any other action at almost any point during the move.

Origin
Engetsuzan is a Zanjutsu technique in the shown in the Bleach anime and manga series, first performed by Byakuya Kuchiki, where the user runs towards their opponent and performs an outwards slash, often dragging their sword along the ground. Notably, Ichigo uses this attack during his fight against Hexapodus, however, Ichigo doesn't dash during the attack.

The game Bleach: Dark Souls has a variation of this attack that closely references the version used in Super Smash Flash 2, with Ichigo dashing before using the slash attack.

Trivia

 * In the manga and anime, this technique was first used by Byakuya Kuchiki to destroy Ichigo's Shinigami power.
 * On the Smash Flash DOJO!!!, this move is called "Shunpō". This is not correct as Shunpō by itself is not a means of attack, but rather the act of moving at very fast speeds.