memories in the rain2 op.3 "Stepping Into Darkness"

Perched above the Hollow Metastacia with Ukitake and Kaien, Rukia offers to strike first, but Kaien asks to face the creature alone and his captain allows it. Before drawing his blade, Kaien demands to know how many Shinigami the Hollow has devoured and whether it feels any remorse. Metastacia mockingly claims his only regret is failing to finish off the female warrior he killed the night before, a taunt aimed at Kaien's late wife. Enraged, Kaien lashes out with startling speed, lopping off two of the Hollow's arms.

When Kaien tries to release his sword, Nejibana crumbles in his hand instead. Metastacia reveals his gift: the first Shinigami to touch his tentacles each night loses their weapon. Battered and disarmed, Kaien is flung aside. Rukia moves to help, but Ukitake holds her back, warning that rescuing Kaien now would kill his pride forever. He teaches her that some battles defend life while others defend honor, and that Kaien is fighting for his men, his wife, and himself. Persuaded, Rukia lowers her hand. Kaien insists his Kidō is enough, yet Metastacia drives the tentacles on his back into Kaien's outstretched wrist, threading into his veins. As the Hollow's body falls apart, it seizes control of Kaien from within, blackening his eyes, greening his skin, and stamping his face with its mask.

This installment ran in Weekly Shonen Jump as "Stepping Into Darkness," but the collected volume and Viz Media instead title it "Affected by the Night." It belongs to the sixteenth volume, Night of Wijnruit, and forms part of episode 49, Rukia's Nightmare. The chapter is the moment Metastacia fuses with Kaien Shiba, setting up the tragedy that fuels Rukia's guilt.