Flashy Flash/Synopsis

History
Flashy Flash was trained in the Ninja Village and participated in the 44th class along with Speed-o'-Sound Sonic. Upon graduation, he was the strongest member of his class, but caused an incident that left Sonic the only other survivor of their class and effectively ruined the village according to Gale Wind.

He left the village after some time. For some unknown reasons, he was hunted by multiple assassins and criminal masterminds but he managed to dispatch all of them during his spare time in his hero's activities. Some criminals and assassins Flashy Flash killed include Aburabozu, the king of organ traders, Harold the drug kingpin, heart collector Burigura, phantom thief Chimagusa, the invincible pirate captain Devil Storm and the higher ups of the Coalition of Assassins.

Alien Conquerors Arc
Flashy Flash appears at the S-Class Hero Association meeting. Although he was at the meeting, he remained quiet for the majority of the meeting. When the Dark Matter Thieves attacked, he left the scene along with other heroes.

Super Fight Arc
Flash appears in I-City where he assists the gathering heroes prepared to fight against Hundred-Eyes Octopus. He uses his powerful speed to rush toward the monster and stabs one of its eyes. After that, he proceed to slash all the eyes of the monster until it goes berserk. As Flashy Flash begins to unleash his special technique to finish the monster for good, Tatsumaki comes in time, lifts the monster up in the air and crushes it into a giant ball.

After the death of the monster, he and the others heroes are berated by her. However, he also proceeds to berate her back, but is stopped by the other heroes. The heroes end up parting ways for now.

Monster Association Arc
The S-class heroes, Flashy Flash, Tatsumaki, Child Emperor, Pig God, Kamikaze, Superalloy Darkshine, Zombieman, Puri-Puri Prisoner and Sekingar attend a meeting and they reassure Narinki that they will rescue his son. They each receive a transmitter that will show their location to each other.

The meeting continues as they plan out their attack on the Monster Association. Flashy Flash gets into a argument with Tatsumaki before Sweet Mask barges into the meeting. When Sweet Mask demanded to take leadership over the S-Class heroes, Flashy Flash taunts Sweet Mask to try and take control with force. Before the argument could escalate further, King arrives and settles the situation. Flashy Flash is suitably impressed with King overnight monster elimination at Z-City. When Sweet Mask backs down, Flashy Flash sighs. Flashy Flash leaves with various other heroes to attack the the Monster Association.

Flashy Flash arrives at the ghost town of Z-City with various other heroes. He compliments Shadow Ring on her ninjutsu and asks where she learned them. Shadow Ring replies not from the same place as Flashy Flash she skitters off. Flashy Flash mentions that it couldn't be his ninja village as his village doesn't train any woman. Flashy Flash kills various monsters from the initial monster attack. After dealing with the monsters on the surface, Flashy Flash heads underground into the Monster Association base alone. There he dispatches several monsters before being confronted by Hellfire Flame and Gale Wind.

The monsters compliment Flashy Flash on his speed before they do battle. During the fight, Flashy Flash destroys the corridor, and Gale Wind rotates one of the blocks they were standing on in order to battle in a more open area. As they fought, Gale Wind explains that they will eliminate all foes who are possibly a threat, and explains the purpose of going after Flashy Flash was because he viewed other ninjutsu masters as rather troubling. Flashy Flash sprints off at speeds neither monsters could track, and he then tells them to unleash their full power as monsters.

Eventually, they are both forced to reveal their monster forms after realizing they are outclassed in their human forms. Flashy Flash's eyes widen in surprise at their increased speeds, and is barely able to block both of their attacks. Round 2 of the battle between the three ninja then begins. They continuing battling, and the two monsters are able to pressure Flashy Flash, managing to make him cough up blood, but once the hero became serious, he strikes both of them with a series of kicks, and then slices both of them in half, ending their lives.

Flashy Flash leaves the battlefield and arrives at a junction. He goes to consult his Locator to see where he is but finds that he lost it in the battle.

Monster Association Arc
He meets up with Saitama, who he mistakes for an enemy. He was very surprised when Saitama was able to dodge and counter his extremely quick attacks. They finally get to where the fight with Garou was going on. Along with Darkshine, his true speed and abilities were shown. He left his mark as perhaps one of the fastest characters in the series, but was ultimately defeated. During their attack on Garou, Zombieman states that even the strength of Darkshine and speed of Flashy Flash would not be enough.

Fall of the Hero Association Arc
By the time the Hero Association is about to fall, Flash acknowledges Saitama's strength, having been among the few heroes who were still conscious during the conflict with Awakened Garou, whilst also feeling that Saitama needs a proper teacher in order to show him how to fully hone his strength. In order to do so, he visits Saitama at his apartment but when Saitama opens the door, he immediately slams it shut before Flashy Flash could properly introduce himself. When King asks Saitama why he did so, Saitama said that it was because "he looked annoying". Flashy Flash however, isn't ready to accept a no and orders Saitama to open the door, because otherwise he would break it open himself. Before he could do so however, he is interrupted by Genos, who demands to know what Flashy Flash is doing in front of his master's apartment, though Flashy Flash tells him that it is none of his business. They start an argument, which quickly escalates into a fight that is stopped by Saitama. Genos then asks Saitama if Flashy Flash is an acquaintance of his, to which Saitama replied with a halting yes. He then introduces Flashy Flash to Genos but says his name wrong, calling him "Forelocks in the face". Flashy Flash tells Saitama that this was just the nickname Saitama gave him earlier and vouches to change this attitude of his. When King tries to tell Saitama Flashy Flash's correct name, the ninja hero stops him as he wants to Saitama remember it himself, because otherwise he will never learn. Genos then asks if he should eliminate him, but Saitama tells him not to, because he would only end up "breaking stuff". Saitama then recalls that he was trapped underground with Flashy Flash earlier and wondered if he had saved him. Flashy Flash then corrects him and tells him that he broke his sword. Saitama asks Genos to grab some tape to repair Flashy Flash's sword but the hero shrugs it off and tells Saitama to focus on recalling who he is. Saitama then tries really hard to remember Flashy Flash's name and is able to recall the first four letters but then ends up spelling it out wrong again, calling him "shoulder blade crush", much to Flash's annoyance. He then changes his mind about his sword getting repaired and asks Saitama if he'll repair it or if he would prefer to pay in cash for it. Saitama then starts to panic and yells at Genos to get the tape, who immediately heads out to buy some. Flashy Flash then asks King to leave as he wants to talk to Saitama in private.

After King leaves, Flashy Flash tells Saitama his real hero name and asks him to become his disciple, as Saitama's abilities are already overflowing with potential but need proper instruction to truly make them shine, since he's not even using half of it in battle. Flashy Flash then wants to start the training immediately and tells Saitama to follow him, but as soon as he leaves the apartment, Saitama slams the door again. Flashy Flash, now at the edge of his patience, returns into Saitama's apartment and tells him to stop messing around, since he hates stupid pranks. He then tells Saitama that the other S-Class heroes are useless and that the Hero Association needs heroes like him (Flashy Flash) who can take out monsters quickly and reliably. He also tells Saitama that he's still growing in terms of strength and that with the right training, he could become nearly as strong as him. Saitama however says that he won't get along with Flashy Flash since he was always calling him by his hero name earlier. Flashy Flash then agrees to call Saitama by his actual name and offers him a deal: If Saitama can defeat Flash in a sparring match, Saitama wins but if he loses, he has to become his disciple.

Saitama agrees and they head out to one of Flash's training sites. Flashy Flash then tells Saitama that in order to win he needs to land only one hit on him and that the time limit will be 30 minutes. In order to give Saitama a little advantage, he lays down all of his weapons. When the battle starts however, Flash almost  loses immediately when Saitama suddenly appears in front of him and almost grabs him, with Flash only barely being able to dodge the move. Flashy Flash than reminds himself that he needs to be more careful since Saitama has already fought toe-to-toe with Garou.

Praising Saitama for almost getting the better of him, he declares that he will not give him another chance to do so. Saitama easily repeats the approach, and Flash again barely dodges the attack. He then uses many of his ninjutsu techniques, evading and attacking Saitama, but doesn't manage to do any damage. Saitama asks him if he can keep up for 30 minutes, as he's sweating and wobbling already, although Flash corrects him mentally, declaring that it's simply cold sweat and exhiliration. He continues the fight, but, frustrated at the lack of damage, lashes out with the ultimate technique Flashy Fist. Chiding himself mentally for going all out like that, he apologizes to Saitama, believing that he hurt him, only for the latter to retort that he is fine. Flash then decides to use his weapons, to better simulate real combat.

He and Saitama continue their combat, with Flash visibly losing his calmness and becoming increasingly nervous at the ease with which Saitama keeps up. Seizing an opportunity to use Slashy Slash, he finds his sword destroyed by Saitama's teeth. Despite using many other ninja weapons and techniques, Saitama is entirely unphased. Flash is eventually driven into a corner, to his own surprise, as Saitama looms in front of him. As he muses over the fact that he doesn't have time to use forbidden techniques, he sees Saitama prepare a punch, and visualizes "Death" in front of him, as Genos had done in his first training spar against Saitama. The training is then interrupted by Genos, who addresses Flash as an "apprentice applicant", and brings news of a monster attack, while a visibly disturbed, sweating and shaken Flash barely responds.