Yushima Oshu had been talented enough to be recruited into the Gotei 13. Naturally, his aptitude was far from poor.
The reason he had seemed so weak in the Ninth Division and become the target of everyone's bullying was because Yushima Oshu had awakened his own Zanpakuto, Ink Moon Halo.
Ink Moon Halo was the only Space-Time Zanpakuto in Soul Society, and its abilities were extraordinarily powerful.
Unfortunately, powerful abilities required powerful spiritual pressure to wield.
With the spiritual pressure Yushima Oshu possessed as an ordinary Soul Reaper at the time, forget using Ink Moon Halo's abilities—even releasing it was beyond him.
While assisting Kiryuo Hikifune in researching Temporary Souls, Yushima Oshu had gained a deep understanding of the techniques for creating Temporary Souls and integrating them into the body.
So, after learning that Central 46 had issued a warrant for his arrest, Yushima Oshu made a shocking decision.
He turned the technique of integrating Temporary Souls into the body to his own use, splitting his soul into Inaba Kagerōza and Kujo Nozomi and escaping Central 46's pursuit.
At the same time, Yushima Oshu had hoped that these two souls separated from his own could use the technique of integrating Temporary Souls into their bodies to raise their spiritual pressure. Then, once Inaba Kagerōza and Kujo Nozomi fused back into him, his spiritual pressure would reach the level Captain Hikifune had possessed when she was promoted to the Royal Guard.
What Yushima Oshu had not expected was that, because his soul had been divided in two, his emotions, memories, and desires had also split into two parts.
Inaba Kagerōza inherited the vast majority of Yushima Oshu's will. He devoted himself to raising his spiritual pressure, restoring Yushima Oshu, and destroying the Seireitei.
Kujo Nozomi, on the other hand, had not