The youngest Advenna Avis immortal, Czesław endured torment at the hands of his guardian, Fermet, who sought to explore the boundaries of immortality. Eventually, Czesław consumes Fermet, thus ending his own agony. Through Fermet's memories, he discovers the horrifying truth that the torture was merely for Fermet's personal amusement. This revelation drives Czesław into paranoia, leading him to distrust everyone and to embark on a mission to consume other immortals before they could harm him.
In the 1930s, Czesław shows little regard for human life, even going so far as to request the execution of a large group of people in hopes of finding an immortal among them. However, after encounters with Isaac and Miria, and being forgiven by Maiza, he ceases his pursuit of other immortals and settles down with Ennis and Firo.
By the 1970s, Czesław begins a quest alongside Maiza to locate the remaining Advenna Avis immortals to inform them of Szilard's demise. In 2001, they discover Elmer living in a secluded village in Europe. After this reunion, they return to New York, while Elmer, Sylvie, and Nile travel to Japan in search of Denkuro.
