Enter . The Fan Theory: The Creator of Sun Breathing? The most popular iteration of the Tenrai-Sensei theory posits that he is not a Hashira, but rather the last surviving student of Yoriichi Tsugikuni —the original inventor of Sun Breathing (Hinokami Kagura).
He is the ultimate "Wise Old Man" trope. In a story where children are forced to kill monsters, Tenrai-Sensei is the grandparent the Corps never had. To be absolutely clear for new fans: No. You will not find Tenrai-Sensei in Demon Slayer: Kimetsu no Yaiba Season 1, 2, 3, 4, or the upcoming Infinity Castle films. You will not find him in the manga by Koyoharu Gotouge. -Tenrai-Sensei- Demon Slayer- Kimetsu no Yaiba ...
Characters like Sakonji Urokodaki (Tomioka’s and Tanjiro’s teacher) and Jigoro Kuwajima (Zenitsu’s master) are former Hashira who now train the next generation. However, they are retired warriors, not all-knowing sages. The fandom began to feel a craving for a figure similar to Master Roshi (Dragon Ball) or Netero (Hunter x Hunter)—a being so old, so powerful, and so eccentric that they exist slightly outside the main political structure of the Demon Slayer Corps. He is the ultimate "Wise Old Man" trope
In this version, Tenrai-Sensei is not helping the Demon Slayer Corps out of kindness, but out of boredom. He has watched the cycle of death between Muzan and the Corps for a millennium and simply wants to see how it ends. He trains Tanjiro not to save Nezuko, but to tie a bow on a millennium-long war he is tired of observing. In the end, Tenrai-Sensei is not a real character in Demon Slayer: Kimetsu no Yaiba . But in the hearts of a dedicated niche of the fandom, he is more real than any Hashira. He represents the desire for history, for wisdom, and for a gentle, laughing grandfather who has seen it all before. You will not find Tenrai-Sensei in Demon Slayer: