Between the cozmez and TCW chapters of Memory, between Nayuta and Tsubaki, it's implied that phantometal erosion either induces anemia, or has effects that are easily taken for anemia. So for Nayuta specifically, it's possible that his poorly-explained illness manifests in part as anemia, but by the rule of conservation of detail, the bout of anemia he has in MEMORy is probably the result of the phantometal trials.