This article contains spoilers for Demon Slayer Swordsmith Village Arc, Episode 11, "A Connected Bond: Daybreak and First Light," streaming on Crunchyroll.
Demon Slayer's hateful fiends are extremely dangerous because of their Blood Demon Arts, which grants them supernatural powers. The Demon Slayer Corps, on the other hand, only has their swordsmanship to match them—and not just any kind of swordsmanship. The most prominent members of the corps train themselves in certain styles, which are referred to as Breathing Styles. Each one attempts to master the said style until they become powerful enough to defeat even the mightiest demons.
Since mastering a Breathing Style is not an easy feat, it's reasonable that members of the Demon Slayer Corps hone themselves in a certain Breathing Style. For instance, the Hashira are the masters of their respective styles. Tanjiro, however, seems to have the ability to utilize techniques from different Breathing Styles, and it has become more apparent in Demon Slayer's Swordsmith Village Arc. While it seems like plot armor, it's actually because of his Sun Breathing.
Sun Breathing Is The Source Of All Breathing Styles
Yoriichi Tsugikunin, the strongest Demon Slayer that ever lived, is the creator and first user of Sun Breathing. Given the Breathing Style's effectiveness in eradicating demons, Yoriichi naturally tries to pass down the art. Unfortunately, there is not one Demon Slayer who managed to follow in his footsteps. Yoriichi then adapts to the situation and modifies the original Sun Breathing, allowing his students to ultimately improve their swordsmanship through these new styles. Those styles are what are now known as Breathing Styles.
While there is nobody who has managed to master Sun Breathing, the art hasn't been lost over time. Yoriichi taught a coal burner the movements of the Breathing Style as a dance—the Hinokami Kagura—which has been passed down from generation to generation. That coal burner is Tanjiro's ancestor Sumiyoshi Kamado. Surprisingly, the dance has been passed down the line with great accuracy, allowing Tanjiro to wield Sun Breathing after receiving swordsmanship training from the Demon Slayer Corps.
Tanjiro Already Has The Foundation For Other Breathing Techniques
After learning about the Breathing Style, Hinokami Kagura has become Tanjiro's strongest fighting style. His years of dancing with his father allowed him to utilize the technique in brief instances, which further allows him to easily grasp specific techniques from the other Breathing Styles.
Since the principles and foundations of the different Breathing techniques are interconnected, Tanjiro's mastery of Sun Breathing serves as a strong basis for learning and adapting to the other Breathing styles. While each technique may have its nuances and variations, the underlying principles remain generally the same. By already grasping these core concepts through Sun Breathing, Tanjiro can transition more smoothly to the other techniques. Of course, that is not to say he can outmatch those who have trained and perfectly mastered the style for years. Even so, it allows him to borrow certain techniques as the situation allows it, which is a powerful card to possess in the world of Demon Slayer.