As far as we have learnt from Vinsmoke Jajji and Ichiji, both used "Wall" during their fight. The moment when they shouted out "Wall," the soldiers immediately formed a line in front of them to act as meat shields for them. Jajji described the soldiers of Germa 66 as the "true backbone of Germa's might" and he expected their absolute loyalty. That was why they obeyed and willing to sacrifice their lives for the sake of their rulers.
It may be difficult for those non-Japanese people to fully understand their culture, particularly their heritage. Many cultures, the past and present, have attributed divinity or significant spiritual gifts to their rulers. The rulers of ancient Egypt and Rome were treated as gods, and medieval kings (including England's Henry VI) were regarded as having the ability to cure diseases with the royal touch.
The Japanese concept of the divinity of the Emperor was not so much of a belief that the Emperor was a supernatural supreme being but rather it was accepted that the Emperor was descended from kami (or gods) who was contacted and inspired by them. Hence the Emperor had the obligation of carrying out rituals and devotions in order to ensure that kami would look after Japan and her people, and to gain assurance of the country's peace and prosperity.
The rituals in the early days became the early practice of Japanese religion (and is still a religion at the present time), Shinto (or 神道), which focuses on ritual practices to be carried out diligently by the Emperor in ancient Japan. In the present day, shrines are established in many places for devotees to go for prayers and worships.
The Emperor of Japan is also called Tennō (天皇), which means "heavenly sovereign", who is the symbol of the country and of the unity of the people. The Emperor holds the highest authority of the Shinto religion as he and his family are said to be the direct descendants of the sun-goddess Amaterasu (or the "goddess of the sun") and his importance besides ruling the country, also lies in dealing with heavenly affairs, including Shinto ritual and rites throughout the nation.
If one can understand the Japanese culture and its relation with the emperors of the country, he/she will be able to appreciate the mentality of the common people with regard to their rulers. An Emperor is the head of the Imperial Family (the emperor and his household undertaking official and public duties of the country) and is the ceremonial head of state of Japan's system of constitutional monarchy, and he is duly respected and honoured, even to the extent of sacrificing their lives when deem necessary. In fact, to be able to die for the emperor would be considered as an honour. Perhaps some of you may have heard the saying, read from books or watch documentaries or movies of ancient stories of Japan where government officials or common people who had sacrificed their lives in order to save their emperors and his family or other similar stories.
Of course those were ancient times and the Japanese people of the present day have become modernised and are very much influenced by various cultures (such as the western culture) of the world. But their ancestry background is still well-maintained and preserved. Obviously most people will not sacrifice their lives for their emperor anymore but they still pay their duly respect and honour to his sovereignty.
Back to our topic of the Vinsmoke family - With the background knowledge of the Japanese culture, we will be able to understand the mentality of the Germa soldiers. The Vinsmokes are the Imperial Family with a kami ancestry and highly regarded. It may seem preposterous particularly for the non-Japanese, but if the story retains the similar precedent background and culture of ancient Japan, then "wall" isn't an ability but rather the call for "absolute loyalty" of the emperor's subjects, which includes the soldiers obviously.
In the same chapter (833), the army of soldiers did not fret, neither did anyone protest over the sacrificial but cheered on when their ruler, Jajji defeated Sanji. In the same token, Ichiji did the same - he called out "wall" and the soldiers formed a line in front of him and blocked the attack from the enemies. The "wall" is like a call for duty which is highly regarded and honoured and hence it is justifiable in the eyes of the entire nation of Germa Kingdom.
On the other hand, if one is creative enough, it can be speculated as an ability, a special power, a skill or a talent such as hypnosis, brainwashing or some form of long term political propaganda that has been instilled firmly to the minds of the nation. Therefore, one being the "sacrificial lamb" for the royalty is as natural as one who dies from illness.
