Here's a breakdown of his key appearances:
Soul Society Arc:
* Episodes 25-31: We see Hollow Ichigo's first appearance in Ichigo's mind, beginning to influence him and show his power.
* Episode 39: Hollow Ichigo fully manifests in a dramatic fight against Kenpachi Zaraki.
* Episode 42-45: Hollow Ichigo actively fights alongside Ichigo, demonstrating his destructive power.
* Episodes 65-67: He clashes with Rukia and becomes a major obstacle in Ichigo's journey to rescue her.
* Episode 71: Hollow Ichigo has a major showdown with Ichigo, where he nearly takes over his body.
* Episode 80-82: He is briefly shown in flashbacks as Ichigo prepares to fight Byakuya Kuchiki.
Arrancar arc:
* Episode 105: Hollow Ichigo briefly appears as Ichigo faces off against Grimmjow Jaegerjaquez.
* Episode 163: Hollow Ichigo's powers and influence over Ichigo become a major focus as he tries to save his friends.
* Episode 168: Hollow Ichigo's connection to Ichigo's inner power is further explored.
* Episodes 174-176: He is shown fighting alongside Ichigo against Ulquiorra Schiffer.
* Episode 179: He makes a final, brief appearance in the fight against Ulquiorra.
Other appearances:
* Episode 1: He is briefly shown in Ichigo's memories as he is granted his Shinigami powers.
* Episode 199: Hollow Ichigo is shown as a manifestation of Ichigo's inner darkness.
* Episode 217: He is briefly shown as Ichigo is struggling with his powers.
* Episode 224: Hollow Ichigo is shown to be in control of Ichigo for a moment, before being pushed back by his human side.
Beyond the episodes:
* Bleach: The Movie: Memories of Nobody: Hollow Ichigo plays a major role, being the source of the film's central conflict.
* Bleach: The Movie 2: The DiamondDust Rebellion: He briefly appears as a manifestation of Ichigo's power.
These are just the most prominent appearances of Hollow Ichigo. He has numerous other brief appearances throughout the series, often serving as a representation of Ichigo's inner struggles and the darker side of his power.