Flashy Flash/Relationships

Saitama
Flash mistook Saitama as a monster and the two had a brief scuffle. After clearing the misunderstanding, the two became acquaintances with one another, with Flash acknowledging Saitama's superior abilities. They soon explore the Monster Association Headquarters together. Flashy Flash gives him the cold shoulder saying he must defend himself and states he would leave him behind if he cannot keep up. Flash finds Saitama irritating but after some time spent together lost in the base, he is impressed by some of Saitama's abilities. This gives Flash some respect towards the bald cape-clad hero but claims he still has much to learn

After being defeated by Garou, Flash was one of the few who retained consciousness and witnessed Saitama defeating Garou. In addition to acknowledging Saitama's strength, Flash decides that Saitama needs a teacher to polish his strength. However, because of his assassin's instinct and mindset, he still looks down on Saitama since he feels that Saitama wastes a lot of his athletic potential and lets his guard down, giving his opponents an unnecessary chance to strike him.

Unfortunately, Flash surprise that Saitama’s power attracts Sonic’s attention when notice his former friend failed to attack the bald hero in few seconds, and Flash grew to respect Saitama and get to know him well in neutral term.

Tatsumaki
Flash and Tatsumaki have an unpleasant relationship with one another, just like with other S-Class heroes. However, he appears to not be afraid of her and is willing to scold her back whenever she insults him. At one point, he insults her powers, saying they halted her physical and mental growth.

Sweet Mask
Flashy Flash does not like Sweet Mask's authoritative and egotistical attitude. While he has some disdain towards some of the S-Class heroes, the tone he gives off is either of annoyance or even teasing, as seen with his interactions with Metal Bat. Flash's displeasure towards Sweet Mask goes to the point of eliciting his murderous intent towards the fellow hero. He goes out of his way to instigate a challenge against Sweet Mask.

Metal Bat
They had limited interactions during the anime and OVAs. However, neither of them could get along with one another. In both moments, Flash would instigate a verbal conflict whenever Metal Bat is talking. This usually ends with Flash mocking Metal Bat and Metal Bat's temper escalating the conflict between them.

Shadow Ring
The two are trained in separate arts of ninjutsu while employing themselves into the Hero Association. Shadow Ring is one of the few heroes Flash shows any respect towards. He complimented Shadow Ring's ninjutsu, even asking her for details of her technique. For Shadow Ring, she is very impressed with Flash's speed. Flashy Flash later on notes that ninjutsu not only comes from his village but also other places, using Shadow Ring as an example.

Superalloy Darkshine
While there was never a true interaction between the two, Darkshine and Flash are known to be a dangerous combo in battle. The two stood together against Garou alongside Puri Puri Prisoner.

Speed-o'-Sound Sonic
Speed-o'-Sound Sonic was Flashy Flash's classmate in the 44th Graduation Class during his time as a trainee in the Ninja Village. Their relationship so far is unknown but Flash is responsible for making him the only survivor of the 44th Graduation Class. During his conversation with Gale Wind and Hellfire Flame, Sonic shows no ill-will toward Flashy Flash.

In the webcomic, it is revealed that the two were actually friends. When Flash was practicing techniques, Sonic decided to approach him and they became friends who relied on each other to keep their sense of morality during the brutal training of the village that encouraged the complete removal of all emotions. The two ninjas bonded, with Flash noting that talking with him allowed him to recover his emotions lost from the Ninja Village training, making it a good experience for him. They both shared a sense of justice and desire to change the institution of the Ninja Village.

When Flash went on a killing spree and destroyed the entire village, he tried to poison Sonic's tasteless stew rather than brutally murdering him like everyone else as a mercy kill. He notes that as he and Sonic were two of the worse students, they had endured even harsher training than others, which is why Sonic is still alive. When Flash found out about Sonic's survival until now after being exposed to the outside world and the bounty on his head (as he is an S-Class criminal), he chose not to hunt him, indicating the strength of their previous relationship.

Gale Wind and Hellfire Flame
Gale Wind and Hellfire Flame were Flash's seniors in the Ninja Village, being from the 37th Graduation Class. The two ninjas desired to kill Flashy Flash due to his ninjutsu talents and causing an incident that killed almost all of the Ninja Village's 44th Graduation Class known as "The End".

Though he initially mocked the two ninjas, questioning what the point of their immense speed was if their brains could not keep up with their actions, but by the end of the fight he displayed some respect towards them while still claiming that they lacked in training.