Hide Away From The Sun

Nejibana drives Rukia across the chamber, its trident ripping the floor from beneath her and calling down crashing waves she can barely block. Landing behind Kaien, she recognizes every trait of his fighting, the raised guard, the spinning, the dance-like traps, as movements her body knows even while her heart resists them, yet she reminds herself that the man wielding them is not the gentle lieutenant she remembers. When he disarms her and declares the fight over, she thrusts a palm into his face and looses Sōkatsui, which he narrowly dodges, blasting a hole through the wall behind him.

His sudden retreat toward a high platform, away from that opening, sharpens a suspicion she has been forming since he first insisted they speak indoors. Convinced he is a fraud who shrinks from daylight, she binds his arm with Hainawa, then chains a double incantation together, pinning his whole body with Rikujōkōrō before firing Sōren Sōkatsui straight through the wall. Sunlight floods in, his borrowed flesh sloughs away, and a glass capsule holding two floating Hollow heads stands exposed as the true Aaroniero Arruruerie, irritated to be seen.

Rukia weathers Kaien's Nejibana and deduces that her enemy deliberately avoids sunlight. Using a Nijū Eishō to combine restraint and attack Kidō, she blows open the chamber wall and floods it with light, dissolving the Kaien disguise and revealing Aaroniero's real form: a capsule of fluid containing two spherical Hollow heads.

Hide Away From The Sun is the 266th chapter of volume 30, THERE IS NO HEART WITHOUT YOU, part of the Hueco Mundo arc. It was adapted in episode 155, Rukia Retaliates! Release the Desperate Kidō.