Elbow Assault

Abridged move description that I paraphrased from the Passport (via Suka Pass):

The Elbow Assault targets the center of the opponent's body with a full-body rush. This area is targeted because this inner area contains many pressure points. The central cord, which runs straight through the center of the body, is especially vulnerable, containing numerous pressure points that are vulnerable to fatal blows*.

However, because this move involves breaking through an opponent's stance and getting inside of his defense, compared to moves used to attack an opponent from the outside, it involves extra risk to the practitioner in that it creates an opening for the opponent to attack. To avoid this risk, the Elbow Assault is executed by raising the hand of the attacking opponent, aiming at the exposed torso and delivering a sharp elbow thrust while stepping inside the opponent's defense. At that time, although the practitioner's body is turned sideways, he must turn his face in the direction of the opponent and observe him carefully.

It seems that Ryo's father Iwao adopted this move from another martial art, but the details of this are unclear.

The "other" martial art that Iwao adopted this move from is Bajiquan, where it is referred to as Liang Yi Zhuang (两仪桩 Yin and Yang/Heaven and Earth Standing) or alternatively Liang Yi Ding (两仪顶 Yin and Yang/Heaven and Earth Elbow). During a trip to China to conduct research for Virtua Fighter, Yu Suzuki visited Bajiquan master Wu Lian-Zhi who showed Yu some moves. You can read more about Yu's research trip through PhantomRiverStone and/or watch a short interview with Yu Suzuki and Wu Lian-Zhi here.

Wu Lian-Zhi demonstrating the Liang Yi Zhuang

You might also recognize it as one of the signature moves of Akira Yuki from the Virtua Fighter series (who practices Hakkyoku-ken--the Japanese name for Bajiquan). As Shenmue was originally developed as a Virtua Fighter RPG starring Akira, this was likely included as part of Ryo's moveset as a holdover. They even have the same input commands in both games. -> -> P

While the Elbow Assault uses a classical form that is a bit too exaggerated to pull off in real life, there have been some applications of it in modern combat sports. It's common for boxers to project their elbows out as a guard and rush through punches in order to get into a close range punching distance or a clinch. In Muay Thai, the vertical elbow can be used in a similar fashion as well as a blatant strike as elbows are legal (Sylvie von Duuglas-Ittu has a good video on it). Former HW/LHW UFC Champion Randy Couture had plenty of success in his fights with raising his elbows and rushing through punches to get to the inside position where he excelled.

Randy demonstrates an elbow counter as an entry into the clinch in his excellent book Wrestling for Fighting.

There are also some examples of committed offensive uses that are more in the spirit of the Elbow Assault. Here is an application of the classical Liang Yi Ding demonstrated by Japanese Bajiquan master Tamotsu Miyahira.

 Clip taken from Tatsuya Naka's Great Journey of Karate 2

Now compare it with this clip of Paul Felder vs Alessandro Ricci. As Ricci throws out the jab, Felder simultaneously avoids the punch and closes the distance while throwing the vertical elbow. Felder's elbow collides with Ricci's face, which stuns Ricci enough for Felder to followup and finish the fight with a flurry of strikes.
 

The Elbow Assault isn't the only move in Ryo's repertoire that's based on moves from Bajiquan and we'll visit the others in a future installment.

*I didn't touch upon the pressure point stuff and don't intend to. Many traditional martial arts incorporate pressure points into their training. As the Hazuki style is a traditional style in-universe with many classical influences, many of Ryo's moves mention pressure points in their descriptions. It'd get too repetitive addressing them each time they're brought up, so I'll only mention pressure points if the description does something different with them other than "hit this and they could die."