Permit me to play with the words a bit, allow me the license to do so for a moment.
Something I have not thought about for a long time is the use of Replacement Stepping.
In the past I defined it thusly.
Replacement Stepping is used to step away from a line of attack.
The stepping leg moves first alongside the other leg, then perhaps because of the attacker moving forward too fast, the other leg steps back to conclude the crescent step. An alternate version has the 2nd leg kick out to form the stance on a different angle, across the line of attack. This can be accomplished by a slide shift if straight stepping is used.
The replacement stepping also moves your centerline from where the opponent desires to strike. This creates a new line to counter-attack. This also works as a force multiplier.
Of course this is just a lot of words. Let’s look at them more closely.
The normal method of moving forward in Isshinryu is the Crescent Step.
That is where the back leg moves in along side the lead leg then moves forward stepping to the outside, the entire stepping motion can be seen as a “C” shape on the floor.
When the crescent step is used it can be thought of using the stepping foot to compress one’s energy into the supporting leg to then explode the gathered energy into the remainder of the step. Thus it can be a force multiplier to increase the energy delivered with a strike at the same time. Or the motion can be used to attack the attackers moving leg in a wide range of options.
But there are other possibilities.
Say the attack is moving faster than you expected, when the foot moves alongside the supporting foot, it can also return from where it came. Thus not stepping as a defense. Allowing you to respond from the original position. There might be tactical reasons for this.
However you are now in a different stance than you originally intended. Now you are in a crescent stance of the opposite shape from your original intention. Likely requiring another response to make that effective.
But another option can be the employment of Replacement Stepping. The attack moving on you is faster than you anticipated, or perhaps you wish to move your center to another location. Either tactical choice can be accomplished with Replacement Stepping.
Thus when your moving leg moves alongside the supporting foot, instead your moving leg now becomes your supporting leg, and the former supporting leg steps back completing the crescent step.
You have gained an immense tactical advantage. For their attack was focused on where they expected you to be. They have moved their center forward anticipating striking you. However, you are not there. Instead you are further back than they expected and the limb they chose to attack with and their body center are forward, perhaps more available for your response.
On the other hand you are in the exact position you wished to be in. and you have moved back in the process. There are a vast number of tactical possibilities that have opened.
The interesting thing is you can practice your kata with Replacement Stepping and not change a movement. Essentially you stay in place for the practice. Also worthy when space to practice is at a premium.
Of course practice of the concept is necessary too. You can do so with any of your kata, without exception. The choice is yours.
I would suggest that only one practice kata is necessary.
I with I had filmed this, but this is one of thousands of things I never got around to filming.
It if of course up to you to work out whether you can do this.
But it adds an entirely different dimention to your possibilities.