Thanks to a fantastic first season, One-Punch Man is one of the most popular anime around. However, there are a number of Original Video Animations (OVAs) that are only available on the DVD and Blu-ray releases of One-Punch Man. These shorts, which exist outside the story's central plot, provide further insight into the One-Punch Man universe.
Here's are some quick synopses of what happens in those shorts, which are absent from legal streaming sites.
"Road to Hero"
With a movie-length runtime, Road to Hero delves into Saitama’s past and the specific events surrounding how he got his trademark mustard-yellow/ketchup-red hero suit. As he continues to grow stronger, Saitama chases down a gang that has been extorting small shops out of business, including the clothing store he frequents for repairs to his tracksuit. Driven by the bounties posted and a need to pay rent, he brings the villains to justice, only to have the landlady kick him out since the crooks were her tenants and a major source of income. The clothing store owner decides to shut down anyway, and he gives Saitama his suit as a parting gift.
"A Shadow That Snuck Up Too Close"
Set before Genos became Saitama's apprentice after the latter defeated Mosquito Girl, the cyborg hero goes to painstaking lengths to uncover the secret to Saitama’s power. After watching a movie on stalkers the night before, Saitama becomes paranoid that he too might have a stalker. Later, Saitama orders a plate of french fries at a diner and returns home. However, this causes Genos to abduct one of the fries, convinced that they might be the source of his power. On the way home, Saitama pummels B-Class criminal Men’s Esthetician Man, thinking he is the stalker, while Genos’ fry sample yields no results at the lab.
"The Pupil Who Is an Extremely Poor Talker"
After Saitama gives Genos a key to his apartment, the two split up to take advantage of a sale for hot pot supplies. However, along the way, Genos loses the key while helping a fallen pedestrian who happens to be a high-ranking member of the Typhoon Family. This then leads to C-Class criminal Don Pacino trying to strike a deal with Genos so as to get information on the Typhoon Family member, for which he'll trade Saitama's apartment key. Genos tells the story of receiving Saitama's key to Pacino, and they eventually realize there's been a misunderstanding. The two fight, and Genos frees the captured man.
"The Ninja Who Is Too Complicated"
After his humiliating defeat at the hands of Saitama, Speed O’ Sound Sonic retreats to a forest to train for their next battle alongside a hunter, who is seeking revenge against the bear that wounded him. While training and taking advice from the hunter, Sonic develops a surprising bond with a boar he names Ino. Saitama eventually arrives and kills the bear, later serving it for hot pot.
"Bang, Who Is Too Overbearing"
After Saitama obliterates a meteor headed for Earth, Bang tracks him and Genos down to assess their strength. He tries to recruit the duo to his Water Stream Rock Smashing Fist dojo by proving his martial arts is superior. Bang beats them readily in a series of contests and games, angering Saitama. However, Bang eventually admits Saitama is powerful, though the hero refuses a place at the dojo in the end.
"The Sisters Who Have Too Many Things Happening"
After the attack by Deep Sea King and his fishmen, Fubuki/Blizzard tries to cope with the news that their group’s efforts in suppressing the threat failed to make the paper. Genos and Fubuki end up on the same train along with a young hero named Swim. They're then attacked by the Serial Bomber. Fubuki, Genos and Swim try to thwart the Serial Bomber's attack. Eventually, they're aided by Tatsumaki/Terrible Tornado, Fubuki's sister, who deals with the bomb without any casualties.
"The Murder Case That Is Too Impossible"
During a hero retreat following the Dark Matter Thieves invasion, Child Emperor investigates the sudden stabbing of Zombieman that happened the night before. He interrogates various heroes, including Saitama, Atomic Samurai and King, in his search for clues. It's eventually revealed that, after Saitama told her she couldn't drink because she looked like a child, Tatsumaki got very drunk and wanted to test Zombieman's immortality by stabbing him with Atomic Samurai's sword.
"Saitama and the Mediocre Ability Users"
Saitama happens upon a group of pitiful villains in a public restroom. After mistaking him for a fellow villain, they attempt to take him down, nearly self-destructing in the process. Saitama ends up saving them, and they change their ways, longing to be respectable top-class heroes. Saitama then saves them again from an attack by Dirt Earthworm. At the end of the episode, Saitama decides to train them.
"Going Fishing with Middle-aged Men"
On a mellow fishing outing, Bang and Atomic Samurai reminisce about the past and what it meant to be a true hero. However, they're attacked by Giant Salamander. Chain'n'toad and Mumen Rider try and take the monster down, but Atomic Samurai is forced to intervene so as to save them. In the end, the two complain about the Hero Association’s commercialization and the bastardization of the essence of heroism.
"Genos and Memory Loss"
An errant backhand from Saitama scrambles Genos’ memory, and the latter hero wakes up with Dissociative Identity Disorder. He says and does things in a very un-Genos way, going so far as to openly flirt with Fubuki and insult Saitama. The Lord of Mountains attacks, and Genos kicks into action, drawing the monster away from civilians. However, he's forgotten how to fight and gets stomped. But after a jolt of electricity, Genos returns to normal, dispatching the monster easily.
"Game and Rivals"
In this OVA, Saitama and Genos participate in an online fighting tournament for a game called "Wild Animals," which has a grand prize of five million yen. Saitama is defeated in the first round by someone with a koala avatar. Garou and Suiryu also compete in the tournament, facing off in an epic battle that results in the latter’s victory. In the finals, Suiryu takes on the same koala avatar that defeated Saitama. In the end, the koala -- which turns out to be King -- defeats Suiryu.
"Puri-Puri Prisoner and the Jailbreaking Prisoners"
During a fight with a monster at Smelly Lid Prison, Puri-Puri Prisoner accidentally damages the prison's electrical system, which allows several prisoners to escape. Puri-Puri Prisoner has a brief confrontation with Speed O'Sound Sonic, to whom he offers a place at Smelly Lid Prison. However, the villain rejects the S-Class hero's offer. Meanwhile, a monster named Urn Eel shows up at the escapees' hideout. Puri-Puri Prisoner arrives and fights Urn Eel, whom the prisoners cheer on. Mistaking their cheers as meant for him, Puri-Puri Prisoner beats the monster and brings the escapees back to Smelly Lid Prison.
"Zombieman Murder Case 2"
Zombieman, Superalloy Darkshine, Metal Bat and Child Emperor are sent to hunt a monster at a snowy mountain lodge. However, the they encounter meet Saitama, Genos, Flashy Flash and Speed O’ Sound Sonic. Learning about his rival’s presence, Speed O’ Sound Sonic tries to hunt Saitama down, but ends up captured by the heroes. He escapes, has a quick fight with Genos which stirs up enough dust to make Saitama sneeze, causing an explosion and power outage that knock out Zombieman. At first, Child Emperor and the S-Class heroes think this must be the result of the monster they're hunting, though eventually they figure out the truth. However, they do end up finding and defeating they were looking for, which is named Crazy Brown Bear.