"Demon Slayer: Kimetsu no Yaiba" was primarily a manga series, and the information available in the story at that time indicated that the characters were not reincarnated in the traditional sense. The manga had not shown any occurrences of characters being reincarnated into new lives after their original ones.
In the series, Nezuko Kamado is Tanjiro Kamado's younger sister. Their bond as siblings is an essential part of the story, and Nezuko plays a significant role in supporting Tanjiro throughout his journey as a demon slayer.
Additionally, the main trio consisting of Tanjiro Kamado, Zenitsu Agatsuma, and Inosuke Hashibira, remained good friends and companions throughout the events of the series. Their camaraderie and teamwork were key aspects of the plot.
However, please note that my information is limited to what was available . There may have been further developments or spin-offs beyond that point, such as new manga chapters, anime episodes, or even official spin-off novels, which could introduce new story elements or alternate universes involving reincarnation or other concepts. For the most accurate and up-to-date information, I recommend checking the latest sources or official releases related to "Demon Slayer: Kimetsu no Yaiba."