Yuuji Sajaki was an Ultra and a member of the crew of the Nostalgia for Infinity. While a chimeric, his augmentations were internal, including a host of medichines. Despite possessing a lithe build, he was capable of the same strength as the bulky chimeric, Hegazi, and was a good deal faster.
During a visit to the Pattern Juggler world of Wintersea, John Brannigan, Sajaki's captain, convinced him to swim in the mind-altering oceans of the alien planet. During his immersion Brannigan manipulated the oblivious Jugglers into overriding Sajaki's mind with a copy of his own, murdering him. Only decades later, after "Sajaki's" death, would anyone discover the truth.
"Sajaki" was a member of the Triumvirate that collectively ruled the Nostalgia for Infinity after Captain Brannigan contracted the Melding Plague. In practice, however, Sajaki captained the vessel, with Hegazi as his lackey and Volyova a minor annoyance.
During the Battle of Cerberus, Ilia Volyova and her partner, Ana Khouri, mutinied and seized control of the vessel. After Sajaki's hand was injured in the coup, he was taken by Dan Sylveste to the medbay. Forgoing more extensive repairs, Sajaki completed his recovery before either of the mutineers suspected. He then contacted Dan and convinced him to leave for Cerberus immediately, with every intention of following.
Unfortunately, Sun Stealer, after confirming the departure of Dan Sylveste for Cerberus and with its mission nearly complete, saw the humans remaining aboard Infinity as nothing more than variables that needed to be eliminated. Before he could leave the medbay, automated surgical equipment linked to the ship -- which was by then under Sun Stealer's control -- violently tore the Triumvir apart.