Since the characters exist in a deterministic universe where all events are known ahead of time, even if the causes of those events change, until Katarina puts on that new outfit and strikes the pose in the ad for Fortune Lovers 2 she is immortal. At some point in the future for the sequel (chapter 22 p.28) to exist Katarina must acquire and wear a black dress with long black gloves, get a black aura, Maria must get a new outfit and two new male characters must be introduced, at which point she will become mortal again.