Heavenly Ninja Party

The Heavenly Ninja Party (忍天党, Ninten-tō) was a party composed of 21 graduates from the Ninja Village from all the different graduating classes. All it's members were wiped out by the duo of Flashy Flash and Speed-o'-Sound Sonic.

Overview
The Heavenly Ninja Party is comprised of twenty one ninjas from the village. Despite the instructors of the village telling the ninjas that any kind of brotherly bond is prohibited, and if they were to encounter each other post-graduation, they were to kill each other, the ninjas of different graduating classes decided to band together, defying those previous orders.

The Heavenly Ninja Party was formed due to these ninja sharing similar beliefs to form an elite assassination squad specializing in combat from generations of graduating classes.

Their main goal is to kill Flashy Flash, who they all hate due to him destroying the village, and to welcome "him" as their leader to publicly kill the aging Blast. Once this is done, they plan to go out of hiding and take over the world with their superior ninjutsu skills.

The majority of the group has been killed by the combined power of Flash and Sonic.

History
After the village was destroyed, many ninjas of the previous graduating classes decided to band together and form the Heavenly Ninja Party out of their shared beliefs and general hatred against Flashy Flash for destroying the village.

Ninjas 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 ninjutsu skills. 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.

Flash and Sonic decide to work together to take down the group and succeed in slaughtering all the attackers.