Heian Shodan is very similar to Taikyoku Shodan, since the latter was, in essence, created as a subset of the former.

It has practically the same embusen of the first Kata, organized in the same pattern: an A-B-A travel with baselines divided into 5 segments. Unlike Taikyoku Shodan, these segments are all distinct.

Segment 1: Gedan-barai Oi-Zuki Baseline (Tettsui variation)

This segment is very similar to the first segment of Taikyoku Shodan. Its most striking aspect is that it is not a mirrored baseline. It starts to the left like Taikyoku Shodan, but the right-side repetition includes an extra technique, a tettsui between the gedan-barai and the oi-zuki. The other baselines of Heian Shodan and most of the Heian Kata are symmetrical, so this one stands out as an exception.

The Heian Kata were incorporated by Funakoshi into his syllabus as his version of Itosu's Pinan Kata, but these have also passed into other styles. The corresponding Pinan kata, Pinan Nidan, exists in Shito-Ryu, Wado-Ryu and Shorin-Ryu, for example, and in all these styles the Kata are mutually very similar, save for some differences in the height of the oi-zuki and the direction of the middle baseline.

Importantly, their first segment differs from Shotokan's in a way that may shed some light. I am going to propose here that, since all 3 styles (and probably more) agree on the basic Kata form, then they are closer to the original, meaning that the differences seen in Heian Shodan are due to Funakoshi's alterations (and not the other way around).

For reference, consult these videos:

https://www.youtube.com/watch?v=XOj4tb5bOOU (Neil Pottinger, Wado-Ryu)

https://www.youtube.com/watch?v=hmpj9_qfY-g (Rika Usami, Shito-Ryu)

https://www.youtube.com/watch?v=xx3yKGbZiK8 (Masters Maeshiro, Takara & Nakamura, Shorin-Ryu)

In Pinan Nidan, the first segment can be described like this:

1. turn 90 degrees to the left in the style's preferred back stance (kokutsu-dachi or neko-ashi-dachi) with a hammer fist (tate-tettsui)

2. advance with straight punch (oi-zuki)

3. turn 180 degrees with gedan-barai to zenkutsu-dachi

4. pull front-foot slightly back, to a more upright position executing a tettsui similar to step 1

5. advance with oi-zuki

6. turn 90 degrees to the left with gedan-barai

The Shotokan version can be described like this:

1. turn 90 degrees to the left in zenkutsu-dachi with gedan-barai

2. advance with straight punch (oi-zuki) in zenkutsu-dachi

3. turn 180 degrees with gedan-barai to zenkutsu-dachi

4. pull front-foot slightly back, to a more upright position executing a tettsui

5. advance with oi-zuki in zenkutsu-dachi

6. turn 90 degrees to the left with gedan-barai in zenkutsu-dachi

The structure is the same in both cases, but Funakoshi's changes have mainly simplified and streamlined the segment, by focusing on zenkutsu-dachi and gedan-barai, thereby reducing the importance of the other stances. By turning the first tettsui into a gedan-barai, Funakoshi introduces the main block of many Shotokan Kata, but he also breaks the symmetry that existed in the original. This is not evident if we look at the movements to the right and left of the starting position (basically, until the oi-zuki). However, if we recall that the turns may be markers for the end of a segment, and indeed a throw before a finishing technique, then the whole segment is composed of 3 movements to the left and 3 to the right. And when we see this, with an allowance for variations in the turns to conform to a convenient embusen, we have a solid symmetry between movements 1-3 and 4-6 in the Pinan version:

• turn with Tettsui

• step with Oi-zuki

• turn with gedan-barai

In Shotokan, this is almost the same, but the first step has a Gedan-barai for the left, and a Tettsui for the right.

So, why did Funakoshi keep the tettsui in the second part? I can only speculate, as I'm not aware of any explanation yet. Perhaps there is something in that Tettsui that was thought to be particularly valid and should be kept for future generations.

I like to think this difference was introduced deliberately to prolong the lesson that is now in Taikyoku Shodan. One possible Bunkai for the first gedan-barai in this baseline is how to deal with a wrist grab. The same meaning can be attributed to the tettsui, and so the second half of Heian Shodan’s baseline can either be an alternative defense for the same attack or a backup when the first evasion fails: if the gedan-barai with a turn is not enough to remove the wrist grab, then we can use a further Tettsui to escape it and double up with an extra attack on top.

In summary, this segment is a non-mirrored baseline:

* Turn into gedan-barai on zenkutsu-dachi

* Advance with oi-zuki in zenkutsu-dachi

* Turn and repeat to the other side, interpolating a tettsui between the turn and the punch

Segment 2: Age-uke Triple Step

This travel is composed of a Triple Age-Uke sequence, and replaces the first travel in Taikyoku Shodan. Like that one, it is an instance of the 3-Fold Repetition pattern. It is more interesting than the Triple Oi-Zuki version in that it teaches a blocking movement that requires coordination of the two hands to clear the path to strike at a vulnerable spot, performed with the forearm. This also shows, clearly for the first time, a "block" technique used offensively as a strike.

Segment 3: Gedan-barai Oi-Zuki Mirrored Baseline

This is a repetition of the mirrored baseline of Taikyoku Shodan. It is interesting to note that it differs from some Pinan Nidan versions where this baseline makes a 45 degree with the main travel, instead of the 90-degree in Shotokan and Shorin-Ryu.

Segment 4: Oi-Zuki Triple Step

This is a repetition of the triple step in Taikyoku Shodan.

Segment 5: Shuto-Uke Mirrored Baseline

This segment is the biggest difference between Taikyoku Shodan and Heian Shodan, and one of the most fundamental segments in the whole Shotokan syllabus. It appears in several higher-level Kata and must be considered, for that reason, a core part of our style. It is a mirrored baseline that introduces the Kokutsu-dachi stance and the shuto-uke and differs from the other by being bent, meaning that its second step is at an angle of 45 degree with the first step.

It is also quite different from the Pinan version, which employs shiko-dachi and a gedan shuto-uke.

Overall, Funakoshi's changes seem to have gone in the direction of simplifying the learning of the Kata, by reducing complexity and creating a systematic core of techniques. It reduces the importance of all stances aside Zenkutsu-dachi, introducing one new stance only in the final segment, and removing or de-emphasising Neko-ashi-dachi, shiko-dachi and shizentai variants), while focusing the shuto-uke at chudan level, since it very rarely appears at other heights in Shotokan. This feels more like a beginner's Kata than the Pinan we can see today in other styles.