Ganryu left----Senna right

Senna
Senna ( lit. drop of madder) is an unusual young woman met by Ichigo and Rukia in the real world. She appears to be a shinigami, but when questioned, she refuses to reveal her identity and evades their questions regarding her squad assignment. Senna wears the standard unseated shinigami uniform, known as a shihakusho, except for a large, red ribbon which she ties around her waist. Her zanpakuto is named Mirokumaru (lit. Maitreya circle) and takes the form of a spear during its released state. When released, Mirokumaru can create tornadoes which Senna can then control to attack.

Ganryu

The Dark Ones
The Dark Ones are a group of spirits that use the "blanks" to fuel their abilities. Using Senna, they hope to collapse both the human world and Soul Society in on one another.

SUMMARY OF THE MEMORIES OF NOBODY

In Karakura Town, unidentifiable spirits called "blanks" (vacant souls) begin appearing in masse. While attempting to deal with these strange souls, Ichigo Kurosaki and Rukia Kuchiki meet Senna, a mysterious shinigami who wipes out most of them fairly quickly. Senna is evasive about her squad assignment, so Ichigo is forced to follow her while Rukia tries to find out what's going on.

Meanwhile, in Soul Society, the real world is suddenly reflected in the sky, so Toushiron Hitsugaya and Rangiku Matsumoto are sent to investigate. They meet up with Ichigo in the real world, who has lost track of Senna by this point. They discuss the events at the Urahara Shop, where Urahara explains the reason for the strange occurrences. As he explains, a soul caught between the two worlds is acting as a conduit, linking them together.

Senna is eventually revealed to be this soul, and a fair amount of the

shows up to deal with the problem. Ichigo tries to defend Senna, but before either side can act, the mysterious group from before shows up. They identify themselves as the "Dark Ones" and set their sights on Senna once again. The many vacant souls wandering around fuel their abilities, making them almost impossible to stop. Despite Ichigo's efforts, they succeed in escaping with Senna.

In a mountainous area, Senna is attached to a strange device, which is fueled by the same vacant souls as the Dark Ones use. As the device powers up, it begins to form a gate with Senna at its core.

Unwilling to give up, Ichigo goes looking around town for her, eventually finding a massive portal sitting on the river. It leads to a strange mountainous region located between Soul Society and the real world. As he enters it, Rukia heads to Soul Society to get reinforcements. Ichigo is left facing the combined might of the Dark Ones, barely able to hold his own.

In Soul Society, Mayuri Kurotsuchi explains to the other captains that the Dark Ones are attempting to break down the barrier between Soul Society and the real world altogether, destroying both worlds. Steps are taken to seal the rift just as Rukia barges into their meeting, begging for help. However, she is turned down by General Yamamoto, and is only able to bring Renji Abarai back with her. At the portal, as Rukia and Renji prepare to enter to help Ichigo, Hitsugaya and Matsumoto appear to offer their help, as well.

Within the other dimension, Ichigo finds himself overpowered by the sheer number of vacant souls the Dark Ones have at their command. He is saved by the timely arrival of Kenpachi Zaraki, with Yachiru Kusajishi hanging from his back. Aside from Zaraki, Soifon, Izuru Kira, Byakuya Kuchiki, Tetsuzaemon Iba, Shūhei Hisagi, Ikkaku Madarame, and Yumichika Ayasegawa have also arrived to help. Along with the four that originally entered the portal, the group makes short work of most of the Dark Ones, leaving Ichigo to battle their leader. Though it takes Ichigo longer, he is victorious, as well.

Back in the real world, all the shinigami exit the portal with Ichigo carrying Senna. Despite having broken the device meant to break down the barrier between the worlds, the process is far enough along that it doesn't go away. As Senna is the initial reason behind it, she chooses to sacrifice herself to seal the portal. She survives doing so, and is taken to her grave by Ichigo so she can pass on properly.