Flame Hashira Chronicles

The Rekidai-en hashira no sho (歴代炎柱の書) is a book that chronicles the rich history of Flame Breathing. The records in the book have been diligently preserved and handed down through successive generations of the Rengoku family.

Overview
The book contains notes written by various Flame Hashira throughout history. The oldest notes date back to the Sengoku period, written by a Rengoku ancestor Demon Slayer who was the first user of Flame Breathing. Passed down through centuries of generations of the Rengoku family, these records have been meticulously preserved until the Taishō era.

The book delves into the origins of Flame Breathing, revealing its roots in Sun Breathing, the original and foundational Breathing Style from which all others have derived. Sun Breathing is described as the very first technique ever created, holding a significant place in the history of Breathing Styles. The book strongly asserts that all subsequent styles are mere imitations of Sun Breathing, deemed blatant copies that are inferior in comparison. It is noted in the texts that practitioners of Sun Breathing traditionally adorn themselves with Hanafuda earrings, further signifying their connection to the ancient technique.

Additionally, the book documented a gripping account of the fateful battle between Yoriichi Tsugikuni and Demon Progenitor Muzan Kibutsuji. Yoriichi himself recounted the clash to the first Flame Breathing user, who diligently penned the account with great detail in the book. However, upon learning the outcome of the encounter, the Rengoku ancestor writes that his confidence faltered, feeling discouraged about the capacity of the Demon Slayers to defeat Muzan in the future. The narrative within the book also mentions Yoriichi's utilization of the supreme thirteenth form of Sun Breathing during the confrontation.

The latest edition of the book is owned by Shinjuro Rengoku and is titled Record of the 21st Generation Flame Hashira (二十一代目炎柱ノ書). However, before retiring as the Flame Hashira, Shinjuro tore apart the book out of anger. After reading the book's content and discovering about the origins of the Breathing Style he had practiced with his entire career as a Demon Slayer, he was overwhelmed by a feeling of inferiority and a profound sense of inadequacy. Shinjuro held the belief that true power and exceptional talent were exclusive to a select few individuals, particularly those born with the innate potential for Sun Breathing. In his view, everyone else, including himself, was regarded as insignificant "riffraff" lacking inherent value. He was firmly convinced that those who still continued to pursue the path of a swordsman without possessing this natural talent, like his son Kyojuro Rengoku, would ultimately meet their demise.

Mugen Train Arc
When Tanjiro Kamado meets Kyojuro on the Mugen Train, he inquires the Flame Hashira about Hinokami Kagura. However, Kyojuro expresses that he has never heard of it. Later, as Kyojuro is nearing his final moments after his intense battle with Akaza, he remembers something from the dream he had while aboard the train and advises Tanjiro to visit his family's estate, known as the Rengoku House. There, he could find some old notes left behind by older generations of Flame Hashira, which his father would often read. Although Kyojuro himself never explored the contents, he speculates that there may be records related to Hinokami Kagura within those notes.

Kaname, Kyojuro Rengoku's Kasugai Crow, guides Tanjiro to the Rengoku estate, honoring his deceased master's wishes. Upon arrival, Tanjiro meets Kyojuro's younger brother, Senjuro, and their father, Shinjuro. Shinjuro immediately recognizes Tanjiro as a Sun Breathing user, triggered by the mention of Hanafuda earrings from the book. Filled with anger, he believes Tanjiro feels superior to them as a practitioner of the original Breathing Style and came to mock the Rengoku family. A brief confrontation ensues between the two, culminating in Tanjiro headbutting Shinjuro and the latter departing from the scene.

Shortly after, Senjuro helps Tanjiro locate the requested book, confident in identifying it since he often sees his father with it. He returns with a book titled "Record of the 21st Generation Flame Hashira", but they discover it has been ripped to shreds and nearly unreadable. Tanjiro inquires if the book was always in such a state, and Senjuro apologizes, explaining that the records are supposed to be well-preserved. Senjuro speculates that his father destroyed the book and expresses his regret that Tanjiro's visit was in vain. However, Tanjiro quickly reassures him, emphasizing that it was not his fault and suggests a different approach. Rather than relying solely on the book, he will focus on training harder to master the Breathing Style. As Tanjiro prepares to depart, Senjuro promises to restore the book, explore alternative sources and consult his father. He assures Tanjiro that if he discovers any valuable information, he will promptly send a crow to inform him.

Infinity Castle Arc
Amidst the intense final battles within the Infinity Castle, Senjuro finds solace in prayer at the Rengoku estate, beseeching his late brother Kyojuro to safeguard Tanjiro. Contemplating a letter he had penned for Tanjiro, Senjuro recalls stumbling upon information within the Flame Hashira Chronicles that might have seem trivial, but could be valuable to Tanjiro. The record reveals a conversation the Flame Hashira of that era had with a Sun Breathing swordsman, who was the wielder of the first Breathing Style, about the latter's encounter with Muzan. The tale shook the confidence of the Flame Hashira ancestor. Eager to share this knowledge, Senjuro conveys the information in a letter dispatched via a Kasugai Crow, which arrives during Tanjiro's clash with Akaza. As the battle had already commenced, Tanjiro must first prevail before he can peruse the contents of the letter. Observing the fierce confrontation from a concealed spot, the crow anxiously awaits.

Following Akaza's demise, Tanjiro seizes a brief respite to peruse Senjuro's letter, absorbing its contents with profound interest. As Tanjiro and Giyu Tomioka resume their journey towards Muzan's location in the Castle, news reaches them regarding the tragic deaths of Muichiro Tokito and Genya Shinazugawa. The weight of this revelation, coupled with the recollection of Senjuro's letter, triggers a deep introspection within Tanjiro's mind. Pondering the description of the first Sun Breathing user's encounter with Muzan, Tanjiro discerns the existence of a thirteenth form of Sun Breathing - an elusive technique beyond the twelve forms he has already mastered.

After Tanjiro lost consciousness due to the heavy injuries he sustained under Muzan's assault, an inherited memory of his ancestor Sumiyoshi Kamado unfolds in his mind. Tanjiro becomes an eyewitness to the extraordinary display of the first Sun Breathing user executing the intricate maneuvers of the technique. In this mesmerizing vision, Tanjiro discerns a profound realization: the thirteenth form alluded to by the Rengoku ancestor in the Flame Hashira Chronicles can be harnessed through the ceaseless cycle of the twelve existing forms he has painstakingly mastered.