Tatsumaki vs. Psykos & Orochi

Tatsumaki vs. Psykos & Orochi is the battle between the S-Class hero Tatsumaki and the leaders of the Monster Association, Psykos and 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 distracting her. Psykos flies down to Orochi's body, confident that if she combines with him her psychic powers will be amplified enough to defeat Tatsumaki. Orochi merges with Psykos, only to reveal that he plans to take control of her instead. After a mental battle, Psykos takes control of the merge and starts to fight Tastsumaki.

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.

Tatsumaki then drags the entire Monster Association Headquarters to the surface, while protecting all the heroes.

Trivia

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