The demon that killed Tanjiro's family is called 'Muzan Kibutsuji'. He is the original demon and one of the most powerful villains in 'Demon Slayer'. His presence instills fear among all demons and humans alike. The tragic night when Tanjiro returned home, he discovered his family brutally slaughtered by demons, with only his younger sister Nezuko surviving, albeit turned into a demon herself. Muzan's influence in the demon world is immense, as he creates new demons and has a unique ability to manipulate their powers.
Muzan doesn't act alone, though. He has countless demons under his command, but they are all mere pawns in his game. The actual demon responsible for the attack on Tanjiro's family is one of Muzan's lower demons, which is never explicitly named, but it's part of a larger revelation about how Muzan spreads his malevolence. This attack serves as the catalyst for Tanjiro's journey as he becomes a Demon Slayer. His quest for revenge against Muzan and finding a way to turn Nezuko back into a human drives the plot forward.
It's heartbreaking to see how Tanjiro’s love for his family fuels his determination. Each fight he engages in is influenced by the memory of his family, especially caring for Nezuko, who's now an integral part of his life. As the story progresses, the impact of Muzan's cruelty fuels the narrative, showcasing how one being's malevolence can lead to countless stories of struggle and loss.
In a way, the story not only focuses on Tanjiro's journey but also explores the connections he builds with others who have suffered under Muzan's reign. Each character fights their own battles, collectively uniting against the darkness that Muzan represents. It creates a beautiful tapestry of emotions, struggles, and alliances that resonate throughout 'Demon Slayer', making it much more than a simple revenge tale. The deep themes of family, loss, and the fight against evil echo in every episode, making the stakes higher with each narrative twist.