NaNaNa Najahkoop serves as a Sternritter within the Wandenreich, bearing the Schrift "U" for Underbelly. His striking visage features spiraling black hair, a crimson mask obscuring his upper face, and teeth aligned like piano keys. During the Soul Society’s initial invasion, he joins Bazz-B and Äs Nödt in ambushing Genryusai Yamamoto, narrowly escaping incineration by the latter’s flames. In the second invasion, he unleashes his Quincy: Vollstandig, manifesting coiled ring-shaped wings, and challenges Sosuke Aizen. Underbelly’s power enables him to dissect an opponent’s spiritual pressure distribution, pinpointing vulnerabilities to generate immobilizing Morphine Pattern grids. This technique briefly incapacitates Aizen—an achievement deemed unparalleled—before Bazz-B’s Burner Finger halts his subsequent attempt to ensnare Shunsui Kyoraku and others. Arrogant and sadistic, he belittles allies and adversaries alike, clinging to fanatical devotion toward Yhwach even after the latter’s Auswählen strips Quincies of their powers. His taunts toward Rojuro Otoribashi and boasts of lethal efficiency mask tactical blunders stemming from overconfidence. Post-war, he endures Bazz-B’s assault only to be apprehended by the Gotei 13’s 12th Division. Confined as Mayuri Kurotsuchi’s test subject in the light novel *Can’t Fear Your Own World*, his narrative influence lingers through Underbelly’s distinct mechanics and his fleeting yet consequential encounter with Aizen.