Speed-o'-Sound Sonic vs. Flashy Flash

I always wanted to settle the score with you someday.'''

Prelude
After receiving a letter of challenge, Flashy Flash splits up with Blast and Saitama to meet with Speed-o'-Sound Sonic at the location given on the letter of challenge. This location is the place Sonic dreamed of putting his own ninja village, which had now become an illegal dumping sight. It is now referred to by Sonic as "The place where dreams end."

Battle
Flashy Flash and Speed-o'-Sound Sonic draw their swords, and both take identical battle stances. The two exchange remarks and Sonic tells Flashy Flash not to get cocky, as he's the one who taught Flashy how to use a blade. After a brief flashback, Sonic and Flashy Flash charge at each other, their swords colliding. After a brief scuffle, the two ninjas jump away from each other, with Sonic taking the opportunity to throw three exploding shurikens. Flashy Flash prepares to block, but Sonic rushes behind him and throws three more shurikens. Flashy Flash leaps in the air to avoid the attack, and Sonic seizes the opportunity to surround Flashy Flash with afterimages using his Ten Shadows Funeral technique, with them all attacking Flashy Flash with Wind Blade Kicks simultaneously. Flashy Flash deduces which Sonic is real and blocks his Wind Blade Kick with his forearm guards. Flashy Flash then retaliates with his ultimate technique, Flashy Kicks. After the attack lands, Flashy Flash praises Sonic for being able to force Flashy Flash to use an ultimate technique, before dodging a bombardment of weapons from the Heavenly Ninja Party.

Aftermath
Their battle was cut short by the Heavenly Ninja Party's attempted surprise attack on Flashy Flash. Sonic gets up from Flashy Flash's Flashy Kicks with minimal damage taken and attacks one of the heavenly ninjas. The Heavenly Ninja Party agrees that Sonic is a traitor and claims they will defeat both Flashy Flash and Sonic. Sonic mentally compares the party to Saitama, claiming that they're smaller than grains of sand. Sonic stands up, claims he's sick of them acting better than him just because their his seniors, and Flashy Flash and Sonic agree to postpone their dual and work together to defeat the Heavenly Ninja Party.

Trivia

 * In contrast to the manga, the fight lasted noticeably longer in the original webcomic.
 * In the original webcomic, both Sonic and Flashy used different techniques and the fight was different too, the only similarities is that the outcome of the fight is still the same.
 * Gale Wind and Hellfire Flame are not seen with the Heavenly Ninja Party, with them presumably dead after Violent Force was sick of them constantly going rogue.