Tatsumaki vs. Psykos & Orochi

Tatsumaki vs. Orochi is the battle between the S-Class hero Tatsumaki and the Boss of the Monster Association's, Orochi.

Prelude
Psykos attempts to fight Tatsumaki by herself, but despite her best efforts, she is eventually overpowered. However, Orochi, having survived the battle with Saitama and absorbed enough monsters to regain his strength, fires his energy blasts from multiple directions with his dragons. Psykos, pleased to see that Orochi survived, flies down to Orochi's body, confident that if she combines with him, her psychic powers will be amplified enough to defeat Tatsumaki. Orochi distracts Tatsumaki with his energy blasts while he merges with Psykos.

Psykos demands Orochi merge with her, but as she's wrapped with his flesh, she realizes that Orochi has been hiding his true power from her all this time. Orochi begins to corrupt her mind, thanking her for her assistance and the countless sacrifices she's given him, but declares he will consume her next, revealing his treachery. Psykos resists, unleashing her mind-controlling powers from her forehead and commanding Orochi to obey her, deeming him nothing more than a vessel while she is the master. The two merge, revealing a new monstrous form with multiple monstrous tentacles and four arms. Psykos managed to take control, expressing confidence in her victory against Tatsumaki, although Orochi, who was able to gain a certain degree of control, speaks through Psykos and declares that he will kill Saitama and use his power to restore himself, and the battle begins.

Battle
Orochi's dragons fire another round of energy blasts, although Tatsumaki easily kills them. Tatsumaki and the two villains clash, the bolts of energy destroying more of the headquarters. The hero notes how much more difficult maintaining her barrier has become, and the fusion increases the gravity around Tatsumaki. Although the female hero proclaims gravity manipulation will have no effect on her, she feels an increased pressure within her barrier.

From the fused body, a larger, white form of Psykos with long, flowing hair emerges, cupping the hero's barrier in her hands. Psykos explains how she switched the inside of the barrier with the outside, corrupting it. Tatsumaki realizes she can't disable the barrier, and Psykos gleefully remarks that the energy she's pouring into the barrier combined with Tatsumaki's own energy output will keep increasing the internal pressure, but also knows that if she releases the barrier, she'll be crushed by the overwhelming gravity. Psykos declares Tatsumaki's flesh and blood won't go to waste, and the female hero beings to bleed from her head and many different parts of her body due to the tremendous strain on her.

However, Psykos shouts in pain, releasing Tatsumaki from her grasp. She notes that a large portion of cells were suddenly eliminated, having been obliterated by Saitama's punch, and also wonders what the slippery feeling was, which was Saitama's bald head. King informs the other heroes that he's secured Tareo and he's heading towards the surface. Tatsumaki, complimenting King's skills, declares that with the child's safety secured, she no longer needs to hold back, and prepares to fight Psykos and Orochi with her full power.

Trivia

 * Orochi's and Psykos's fused form is designed based on neurons..