Ninja Village

The Ninja Village (忍者の里, Ninja no Sato) is the hidden ninja village located somewhere in the World and it is the hometown of Speed-o'-Sound Sonic, Flashy Flash, Hellfire Flame and Gale Wind. The location of the village is unknown. According to Flashy Flash, the village is all male.

Hellfire Flame and Gale Wind are the graduates of the 37th class and were among the top of that class, while Sonic and Flash are the sole survivors and graduates of the 44th class, with Flash being the No. 1 of the class. Flashy Flash is responsible for the deaths of the 44th Graduation Class and the entire village in general, known as "The End," and all the ninjas of previous graduating classes regard him as a criminal.

All Ninjas from The Village possess extreme levels of speed. Wind Blade Kick is a technique utilized by both known members of the 44th Graduation Class.

Overview
The Ninja Village is a very horrible and utterly despicable place. This is because children under the age of 7 are sent at a young age to this ninja village, where they are trained for 10 years under extremely ruthless conditions, and then sold off to factories of the underworld. Escape from the village is impossible, and ninjas may only leave when they complete the curriculum and obtain permission to graduate. The children are worked for 72 hours a week, with only 6 hours of sleep. The food is tasteless, and any information from the outside world is completely cut off. Any kind of emotions are not allowed to be expressed, and those who lose their emotions gained excellent ratings. Additionally, companionships and a sense of brotherhood among the classes is not allowed, and even talking amongst one another is prohibited. Instructors went so far as to say that if they ever crossed paths in the future after graduating, they were to try and kill each other. Flashy Flash correctly described it as a hellish environment. Despite this, many of the ninjas hold resentment against Flashy Flash for destroying the village and plan to kill him because of it, showing that they still respect the village.

The training regiment is extremely arduous, and the ninjas are separated into five classes of training based on their skills. Class One is reserved for the most powerful ninja, and people in this class receive the most lenient training, while ninjas in Class Five receive the harshest training.

Although unconfirmed, it can be assumed that since Sonic was one of the weakest ninjas of his class, many if not all of the other ninjas that graduate from the village have capabilities that are Class S.

History
Sometime in the past, the ninja village was founded by a man regarded as the most powerful ninja to ever walk the earth. From this point on, several ninjas were trained in separate graduating classes and were sent to factories in the underworld.

About 20 years ago, Flashy Flash was sold by his parents at the age of 5 to the Ninja Village. Throughout his childhood, Flashy Flash was consistently pushed to his limits and kept alive through specially formulated medicines. Eventually, he decided to purposefully perform badly in order to receive the harshest training in Class 5. Sometime during his training, he ran across Speed-o'-Sound Sonic, and the two bonded due to both of them being in Class 5.

Sometime during this period, the leader of the ninja village challenged Blast and was defeated. Although Blast didn't kill him, the leader was put in a coma, and the ninja village placed him in a regeneration chamber to speed up his healing.

Several years passed, and by the time Flashy Flash was 16, he'd long chosen to stop hiding his abilities and was ranked number one. Unbeknownst to the village, however, was that Flashy Flash had begun to develop a sense of justice and hatred against the evilness of the village. With his fighting abilities becoming formidable enough, Flashy Flash went on a rampage, killing the instructors, staff, fellow members of his class, and basically everyone who was a part of the evil village. For some reason, Flashy Flash either could not or chose not to kill the leader of the village, possibly because his location was hidden from Flashy Flash or that the hero thought he would be too powerful to kill, even while in a coma. The only one who survived was Sonic, who had been poisoned by Flashy Flash as a mercy instead of brutally killing him, although thanks to the brutal training he endured being in Class 5 all of his life, he managed to survive.

After the village was destroyed, many ninjas of the previous graduating classes decided to band together and form a group known as the Heavenly Ninja Party. Their main goal is to kill Flashy Flash, who they all hate due to him destroying the village, and to welcome "him" (the leader of the ninja village) as their leader to kill the aging Blast. Once this is done, they plan to go out of hiding and take over the world with their superior ninjitsu abilities.

Fall of the Hero Association Arc
After Sonic is once again defeated by Saitama and is recovering, he is approached by the Heavenly Ninja Party. This party consists of ninjas from previous graduating classes of the village, including Gale Wind and Hellfire Flame, and reveal to Sonic their plans to kill Flashy Flash and Blast, make the leader of the ninja village their leader, and come out of the shadows to take over the world with their superior ninjitsu abilities. They tell Sonic to lure Flashy Flash out, where they'll ambush and kill him. They also warn him that those who betray them will be executed. Sonic, being outnumbered, has no choice and complies to their plan.

Sonic lures out Flashy Flash, and the two begin to battle. As they fight, Flashy Flash is impressed by how much stronger Sonic has become. Sonic states that he's not the same fighter from several years ago. Flash realizes this, and concludes that he has to use his ultimate moves to defeat him. It is at this point that the other ninjas attack Flashy Flash simultaneously with their weapons. The hero is able to dodge all the weapons, but is surprised by the number of people there and asks what this is all about. The fighters reveal themselves as ninjas from the village and their plan to kill Flashy Flash. But then, Sonic attacks one of the ninjas. He goes on to say that he could handle Flashy Flash, and for them to get out of his way. The ninja reveals his Ten Shadow Burial, impressing all of the ninjas watching him. The hero then decides to silence all the other ninjas, and their battle begins.

Trivia

 * Every known ninja from the village has a redundant name for unknown reasons.
 * There are other ninja villages in the world, such as the one Shadow Ring trained at. According to Hellfire Flame and Gale Wind, none of the other ninja villages are nearly as powerful as theirs. This can be due to the survival-of-the-fittest graduation procedure, which only the best of the best are allowed to be full-fledged ninjas.