Eijiro Kirishima & Taishiro Toyomitsu vs. Kendo Rappa & Hekiji Tengai is a battle fought between the Pro Hero Fat Gum & his trainee Red Riot against Shie Hassaikai members Kendo Rappa and Hekiji Tengai of the Eight Bullets during the Shie Hassaikai Raid.
Sir Nighteye and Fat Gum's squads continue through the Underground Labirynth after leaving powerful villains to Suneater. Red Riot worries about his friend but Fat Gum reassures him that Tamaki can handle himself.
Fat Gum pushes Eraser Head out of the way in time, but Red Riot tries to do the same and their both sent through the hole. They tumble down a cave and end up in another room, where Kendo Rappa and Hekiji Tengai are waiting for them. 
Rappa swiftly attacks with a vicious flurry of punches that rain down like hail on the two heroes. Red Riot notices the initial punch and defends himself with his Super Move: Red Riot Unbreakable. Rappa's bullet punches send Red Riot flying into the rear wall while Fat Gum withstands the blows. They're both shocked to see that Red Riot's Super Move was easily broken.
Fat Gum quickly counterattacks with a punch, but Tengai protects Rappa with a barrier tougher than steel. He lowers it and allows Rappa to unleash another barrage of bullet punches. Rappa's surprised to see that Fat Gum is capable of withstanding the punishment. Fat Gum doesn't recognize either of the villain's Quirks and assumes they operate outside the organization.
Tengai compares the current skirmish to a brawl between spears and shields. Rappa and Tengai are a spear and shield while Fat Gum and Red Riot are a shield and a shield. However, Eijiro is injured and appears to be lacking as a shield. Fat Gum reassures Red Riot that the fight is not lost yet and Rappa is excited that the heroes are trying to win despite the stalemate. 
Rappa demands Tengai stop using the barrier because he believes their combo was forced on them by Overhaul. Tengai reminds his partner that Overhaul is their master and they must obey because this matchup favors them. Rappa disagrees and tries to attack Tengai, only to have his punches nullified by a barrier shield. Rappa quickly turns his attention to Fat Gum and gets into range too fast for the pro to dodge. The villain uses his Strongarm Quirk to barrage Fat Gum with rapid-fire punches and deals damage to him in spite of his Absorption Quirk.
Fat Gum knows he has to take Tengai out of the match if the heroes have any chance at winning. Fat Gum baits Rappa's battle-hungry nature and challenges him to a slugfest. Rappa unleashes a seemingly endless rain of bullet punches and breaks through Fat Gum's defenses. Eijiro watches helplessly as his mentor appears to get beaten down.
Rappa pleads with Fat Gum to keep fighting while the BMI Hero secretly plots against him. Fat Gum's body fat is burning away as it rapidly absorbs all of Rappa's powerful blows. However, the energy created from burning away the fat can be redistributed into a spear that can break any shield. Tengai realizes that the hero is plotting something and tells Rappa to desist, but the battle-crazed fiend refuses. Fat Gum took more damage than he anticipated, and can't redistribute the exact same amount of power. Before Rappa beats Fat Gum beyond his limit, Red Riot suddenly rushes to protect him.
With his resolve restored, Red Riot withstands Rappa's barrage by re-hardening his body the instant his hardening Quirk gives. With this, he's able to stand his ground and even impress the villain with his strength. They both throw punches that would collide if not for Tengai putting up another barrier to protect Rappa, much to the latter's displeasure.
Tengai believes Red Riot is out of options against the barrier. Fat Gum argues that Red Riot's service as a spear was exactly what their team needed. Fat Gum's fat burns away and reveals his true form as he's now armed with tons of shock absorbed from Rappa's offense. 
Sensing Fat Gum's incredible power, Tengai creates a barrier of maximum size and strength. Satisfied, Rappa states that the barrier just going to break no matter what. Fat Gum attacks with the full power of his manly heart. He claims the villains are going to lose because they underestimated Red Riot. Fat Gum carries Red Riot to victory and finishes off the villainous duo with a powerful punch that shatters Tengai's barrier and sends them both flying.
With the villains defeated, Fat Gum checks on Eijiro's condition and notices him fading out of consciousness. Eijiro wearily claims that he'll protect his mentor. Fat Gum recalls Eijiro first requesting to work under him because he wanted to be a hero who could be brave enough not to stand by when people are in danger.
The flashback is interrupted when Rappa manages to get back on his feet in spite of his broken body. Worried, Fat Gum realizes that he can't fight with his Quirk completely worn out. Rappa asks that Fat Gum tend to Red Riot's wounds so they can fight again, referring to him as a man. This surprises Fat Gum and Tengai pleads with Rappa to stop acting selfishly. Tired of arguing, Rappa stomps on Tengai and knocks him out.
Rappa claims that Tengai can no longer fight and admits he can't anymore either. Fat Gum asks what Rappa desires and the villain responds he wants them to violently fight to the death. He came from an underground fight club where fighters could use their Quirks as much as they want. Rappa was too strong for his own good and ended up defeating everyone without so much as a challenge. He demands that Red Riot heal so they can fight to the death.
Fat Gum refuses and says the villains lose and are going to be arrested. Rappa claims its a draw because nobody is dead and leads them to an infirmary because he wants to fight Eijiro again man to man. Fat Gum took in Eijiro because he knew his own weaknesses. Proud, Fat Gum looks over Eijiro's unconscious body and tells him that he's a man recognized even by the enemy.
Rappa tells Fat Gum the story about how he ended up working for Overhaul. He lost to him in a fight while getting recruited and has been apart of the Shie Hassaikai ever since while trying to defeat him. Rappa even reveals that Overhaul is plotting to reinstate the Yakuza by spreading his influence using something special, and the day he's carrying it out has come.