The War for One Man
At the time, the Gotei 13 leadership had suffered heavy losses. Some Captains simply resigned from their positions. Others, however, had disappeared and were subsequently reported MIA. The numbers had dwindled down to a select few: Saibo Tsubaki (8th Division Captain), Nonko Ryuuza (12th Division Captain, Gunpei Moromashi (11th Division Captain), Hideki Sahashi (4th Division Captain), and Takehiko Rokujo (Captain Commander).
It was speculated that these disappearances were largely in part due to a man known simply by the name of Teisuke. This dangerous individual was incredibly powerful, and was actually the individual who had killed Nonko in his human life. He is not by technical definition a Shinigami, as he had never been in contact with an Asauchi. Rather, his Zanpakuto was obtained by killing another Shinigami and enslaving its Spirit by forcibly imprinting his own Soul on it. He eventually came across a spiritual black market known as the Underground and assumed control of it, transforming it into something akin to a spiritual Mafia. Left unopposed for a time, he eventually became a serious threat to the Gotei 13, as his actions were drastically throwing off the Balance of Souls. Nonko had suspected such things from Teisuke from the beginning, and it was not long before his research validated h is suspicions. Knowing that someone would catch on eventually, Teisuke began to make his move . Nonko's instruments detected a large concentration of spiritual energy in the human world, and further inspection revealed that the source was a massive invasion of Hollows.
After Nonko alerted Takehiko to the invasion, the Captain Commander issued two orders:
1) All remaining Captains were to assemble at the Senkeimon, and prepare to enter the World of the Living to combat Teisuke and the massive Hollow invasion.
2) The Vice Captain or highest ranking officer of each division was to assume command of their respective Divisions.
After the Captains were assembled, Takehiko informed them that the limiter would not be in effect, and that there would not be a restriction p laced on Bankai. Combat would be expected the moment they entered the World of the Living. While the combat force was made aware of the massive Hollow thread, this was made the second priority. The primary objective was to eliminate Teisuke at all costs, and only after success on that front, to eliminate any Hollows in the area.
Once they entered the World of the Living, all they saw was rampant chaos. Teisuke's troops from the Underground were tasked with grabbing the attention of any Captain-Class combatants. This was achieved by killing, destroying buildings and recreational areas, and causing mayhem across Karakura Town. The humans of the newly established Phoenix School knew they stood no chance in this battle, and were left the task of evacuating the regular citizens. They did so by pretending the destruction was being caused by some sort of storm, using their own powers to create the illusions of nasty weather. The Quincy in the area were already doing their best to contain the Hollows, while the Phoenix School evacuated the citizens. Explosions, fires, and collapsed buildings were becoming more common, as the fighting continued, but not a sign was seen of the other two Factions: The Vizards of Viz-Corp, nor the Arrancar of Las Noches.
The Human Struggle and Cowardly Company
In the aftermath of the Arrancar Invasion, Clyde an d Drystan were working frantically to create an organization that would be able to aid the Spiritually Aware humans who stood on the edge of the constant war between the two spirit worlds. Working out of the Manga Shop that had been left to them by the mysterious Hasaki Ryo, the two young men began to train those who could see spirits to defend themselves, in the hopes that they would not have to rely on the Shinigami for protection any longer. Before they could begin to come close to such a goal however, the World of the Living was thrown into chaos by the arrival of Teisuke, and the mass of Hollows and soldiers he loosed upon the town. When the remaining Shinigami Captains had come to deal with the threat, and began to focus their efforts on the ring leader, Drystan realized how hopelessly outclassed they were. Organizing himself with Miwa Kiyomizu, and Clyde, Drystan used Alchemy, and Miwa's ability to control electricity to create the elaborate illusion of a monstrous storm to explain the damage being caused by the Hollows and the soldiers. Clyde convinced the Quincy to try and contain the Hollow as best they could while their new School focused on evacuating citizens from the "storm".
Meanwhile, Drystan went to seek out the Vizard Council for aid. However, he arrived at Viz Corp HQ to find it abandoned, its great leader Kuro Akuma nowhere to be seen. Checking the Spaztic Reality nightclub as well, Drystan found only a lone Fullbringer who had allied with Kuro named Shakan, and convinced him to help with the evacuation effort. As their evacuation came to a conclusion, the united Human faction could only hope the Shinigami Captains were enough to handle Teisuke...why else would they focus so intently on him?
Castle on the Dunes
While these events took place in the World of the Living, days were going by faster in Hueco Mundo. Over the course of the battle for Teisuke's head, tensions in Las Noches had risen to dangerous levels, and the Espada were rebelling against the Lord of the Deep; Karzan Zaraki. All Espada but one were united against him, lead by Kyoshin Oscuro the former Second in Command to Karzan. Having anticipated and even planned for these events, Karzan was not surprised when Kyoshin challenged him, and he willingly accepted the battle. Their battle was long and fierce, but eventually they both grew tired, evenly matched as they were.
Taking advantage of a lull in the fighting, Karzan flared his Reiatsu, both a signal to Nero waiting outside, and a way to keep his former subordinates in check while he made his escape. Howling loudly, he paralyzed the assembled Espada and sealed his Zanpaktou. He passed the throne on to Kyoshin with little more than a passing remark, claiming that their usefulness for him had ended.
When the Espada finally recovered from his paralyzing howl, they rushed to try and intercept him, but they found the entrance to Las Noches blocked by Nero's silver flames. They could do naught but watch as their two enemies wandered off into the vast sands of the Moonlit Desert.
The Final Step into Madness
No one knows what motivated him, but during the battle with Teisuke, Gotei 12th Division Captain Nonko Ryuuza had been preparing a Reiryoku bomb in preparation to kill Teisuke, and to mask his own plans. Detonating the bomb at the peak of the battle, Nonko indeed succeeded in destroying Teisuke, but in the process masked his own defection. The Reiryoku bomb devastated the Universe with its shock waves, extending all the way to Soul Society and Hueco Mundo, shifting Reishi particles and causing the energy in all beings who had Reiatsu to shift and release. This lead to most if not all Spirits an d spiritually aware Humans losing a vast portion of their powers, only those with considerable strength of will managing to hold on to their lives in the process. The madman Nonko has not been seen since this day, and it would 30 years in Soul Society before the Captain Commander would finally order an investigation.