During the Siege of Dejagore, like the rest of the Nar, he was loyal to Mogaba. After the siege, he was one of the 12 Nar who accompanied Sindawe in abandoning Mogaba publicly to return to Croaker, the genuine Captain.
Although Isi's Company rank was unspecified (presumably, sergeant), he was a general in the Prahbrindrah Drah's Taglian army, answering directly to Lady, who was the Company's Lieutenant (second-in-command).
By the time the Company reached the shadowgate in She Is the Darkness, only Isi, Ochiba, and Sindawe remained alive of the 13 Nar who rejoined Croaker. All three of them join the Company leadership when they attempt a scouting mission across the glittering plain. Isi and Ochiba became members of the Captured when Soulcatcher sprang her trap at the fortress with no name.
Isi, Ochiba, and the rest of the Captured remained in the cave of the ancients, untouched and unconscious, for at least 15 years. Isi was identified by Sleepy and her rescue party, but, because of time and resource restrictions, he was not among the first 5 people liberated during her first wave of rescues.
Isi and Ochiba were not mentioned in the Annals by name again, so their specific fates are not known. But, according to a blanket statement recorded by Sleepy, they were among those released from their stasis by Company wizards during one of Sleepy's subsequent expeditions back and forth between the nameless fortress and the Company's new headquarters, the Abode of Ravens in Hsien. Isi presumably participated in the creation and training of the Company's new army, recruited from Hsien. It is also known that, less than five years after Isi's liberation (toward the end of Soldiers Live) Croaker noted that only he (Croaker) and Lady remained alive of the Captured. If this is accurate, it meant that both Isi and Ochiba either died sometime either during the four-year gap between Water Sleeps and Soldiers Live (like Otto and Hagop, who died of natural causes in peacetime), or, more likely, during combat in Soldiers Live (such as, the Battle at the Shadowlander cemetery or the Siege of Taglios).