Koichi Hirose appears in select episodes of the spin-off "Thus Spoke Kishibe Rohan," supporting the central narratives. In "Episode 16: At a Confessional," Koichi proactively seeks Rohan Kishibe's aid to learn Italian. He specifically requests Rohan use his Stand, Heaven's Door, to implant the language knowledge directly, demonstrating trust in Rohan's abilities despite their past. Koichi makes a brief, non-speaking appearance in the "Rohan au Louvre" chapter, depicted visually among tourists inside the Louvre Museum, separate from Rohan and the main story. He accompanies Rohan to Mutsu-kabe Shrine in "Episode 2: Mutsu-kabe Hill," joining the investigation into local rumors as a companion. While providing a familiar connection, the episode focuses on Rohan's experiences there, with Koichi's role lacking significant development or unique actions. Koichi remains absent from other episodes like "Millionaire Village," "Poaching Seashore," "The Harvest Moon," "Deoxyribonucleic Acid," and "Hot Summer Martha." His established traits—politeness, underlying courage, and willingness to assist allies—persist consistently but receive no new exploration or unique narrative focus within the spin-off beyond his documented appearances.