Assault on Tartarus

The Assault on Tartarus is the attack organized by All For One within Tomura’s body to retrieve his original body from Tartarus prison, employing the seven Near High-End Nomu and Tartarus' own prisoners.

Prologue
The heroes organized an operation to take down the Paranormal Liberation Front and arrest their members, however it ended up triggering a conflict for which the result was disastrous for the heroes: a slew of heroes died fighting the villains and even more ended up maimed, hundreds of civilians were killed in the midst of everything despite evacuation orders, and society's faith in heroes begins to crumble. The vast majority of the PLF soldiers were captured, but several of them managed to escape, one of them being the leader of the organization, Tomura Shigaraki, although he did not do so without some "help".

After an intense fight against the heroes, the will of All For One within Tomura Shigaraki takes over his body, and against the wishes of his protegee, he uses his Quirks to command a group from Near High-End Nomu to help him escape from the battlefield. Despite the heroes' attempts to stop them. All For One manages to escape with a few allies and seven Near High-Ends. However, All For One does not intend to let the heroes to take a break, so within hours of escaping the battle, he commands the Nomu to free his real body from Tartarus.

Battle
Gyges and Briareos, along with numerous Prison Bots, stand guard at the Bronze Gate, the mainland entrance to Tartarus. The two heroes are discussing the terrible outcome of the recent conflict against the Paranormal Liberation Front, when suddenly the prison bots are activated. Gyges is about to check the security system when he sees something approaching. To both heroes’ shock, they turn out to be three Near High-End Nomus.

Briareos immediately orders the prison robots to fire, at the same time as he and Gyges takes their miniguns to attack them as well. One of the Near High-End creates a force field to protect themselves from the gunshot. Another of the creatures steps forward, inflating itself until it shoots spikes that run through its body. The projectiles hit Briareos, killing him instantly.

A guard in the monitor room tries to contact Gyges and Briareos. Under intense fire from the Tartarus security robots against the Nomu, Gyges reports that they are under attack, and that his brother Briareos was killed. Being aware of the threat he faces, Gyges requests the code red security alert to be activated immediately.

Shielded from robot bullets by the Near High-End Nomus, All For One comments how uninspiring the situation is, before unleashing the power of his Quirks, obliterating the guard post, allowing him and the Nomu to trespass the destroyed Bronze Gate.

Still surprised that the Nomus came there directly from the last battle, the prison guards immediately activate the code red: the floors of the prison get sealed off, the bridge between the Bronze Gate and the prison is lowered, and the Cottus drone squad is deployed to attack the the intruders. All For One comments that their efforts are in vain.

A group of Near High-End Nomus who are hiding underwater emerge to attack the drones, as All For One flies over the chaos on a flying Nomu, having an internal argument with Tomura's manifestation, who refuses to be his pawn and demands his body back again. All For One listens to every word, but he is quick to remind Tomura that he is the one who wanted this power for so long, and also he is not a pawn but the next him.

All this discussion happens when they are detected by the security robots, which do not stop shooting at them. All For One uses Decay to destroy the guard tower, escaping from the attacking robots. Then he uses Search to find his body located in the deepest level of the underground prison, about 500 meters below sea level. All for One is aware that if he used the Decay to destroy the prison, even though he could control the wave so as not to destroy his original body, the pressure hundreds of tons of seawater would kill him, not to mention Tomura’s body is starting to fall apart faster when he uses Decay.

Recognizing the efficiency of Tartarus security systems, All For One comes with the idea of a fully coordinated attack both inside and outside the prison, at once, by taking advantage of the link between his real body and the manifestation that controls Tomura's body at that moment.

Inside his cell, the real All For One uses an EMP like quirk to disable the prison electronics, deactivating as a result the restraints and locks throughout the prison. During all of this, those also in the prison are able to break out of their cells as well. Suppression squads immediately head out to deal with the incoming threats, and some of the inmates are shot dead, but it soon becomes clear that they will not be enough to stop the most dangerous ones.

The now released Muscular breaks into the monitoring room. One of the guards stationed there begins to shoot him, but the villain is not affected by the bullets thanks to his Quirk and crushes him, asking the rest of the guards about how to get out of there. Meanwhile, in one of the corridors, the villain Moonfish uses his Blade-Tooth Quirk to easily take out a suppression squad, not caring that his attack also kills several of the prisoners who were also trying to escape. Lady Nagant notices the prison falling apart and notices another door, which she opens and ends up letting out Kai Chisaki, who quickly runs out calling for his boss.

Little by little, the convicts take control of Tartarus.

Aftermath
Tartarus is now overrun by the villains, but they find out they cannot reach mainland because the jail's bridge is under water. However, the solution to this problem seems to appears when All For One comes out, telling the convicts to submit to him if freedom is what they seek. All For One had managed to escape from his cell taking advantage of the prison break, meeting with Tomura shortly after. All for One says that the impending void era will give rise to a more perfected demon lord, and that this will be the story of how he will become the greatest demon lord of all.

To escape from Tartarus, All For One takes command of a series of emergency aircrafts, and since they use the official Biometric I.D to be operated, he and his new allies, takes the pilots as a hostage, telling him to follow his orders. His plan to free himself from Tartarus has worked perfectly, as the all-powerful villain is now standing freed with and army of convicts. For the next six hours after the prison break, the real All For One sends the Nomus and the escaped prisoners to attack seven other prisons, freeing additional villains and criminal from six of them. Attacking a series of prisons didn't just work to make it harder for the authorities to track him, but also to increase the crisis and fear in society, generating even more mistrust and rejection of heroes.

Meanwhile, All For One within Tomura’s body orders Dabi, Spinner and Skeptic to watch over him while he rests, as Tomura's body needs time to recover from the injuries received during that day. Spinner looks bewildered, telling him he’s not the one he chose to follow, but All For One assures him he has the best intentions for Tomura’s wishes, and once the body is perfected, their desires will be achieved.

Manga & Anime Differences

 * The anime shows the initial attack on the Bronze Gate.