Tanjiro Kamado is not related to Muichiro and Kokushibou. The Kamado family are descendants of Sumiyoshi, one of Yoriichi’s closest friends, but since Sumiyoshi and Yoriichi aren’t related, neither are Tanjiro and Kokoshibou. On the other hand, Muichiro is a direct descendant of Kokushibou.
Namely, Tanjiro couldn’t have met Kokushibou since Kokushibou is much older than Tanjiro, and there is no direct family relationship between them.
Is kokushibo a demon?
Kokushibo is a major supporting antagonist in Kimetsu no Yaiba. He was a Demon affiliated with the Twelve Demon Moons, being the only one who held the highest position, Upper Moon One. Before his death, he was a powerful swordsman and one of the closest servants of the Demon King, Muzan Kibutsuji, whose main purpose was to aid him in seeking the Blue Spider Lily. Before becoming a demon, his.
This begs the query “Is kokushibo stronger than Muzan?”
Yet Kokushibou is fighting several pillars at once without even a scratch on him or pushed to the limit. Muzan fucked up cuz he was taken out by an unexpected attack plus Tamayo’s drug weakened him. Kokushibou is strongest among all demon cuz he is no 1 but not stronger than Muzan. After all they all become demon cuz of him.
Kokushibo is also newly added to the game as the current final boss of the Slayer Storyline. He also has a chance of dropping Kokushibo Blood when killed. If you drink it it changes your demon appearance to six eyes instead of two. He has been added in the Patch 2.5.
Moreover, why did kokushibo become a demon?
Out of fear of death, Michikatsu became a Demon and took on the name Kokushibo. Because he was also Breath user, it took him three days fully transform into a demon. Eventually, he became Upper Moon One of the Twelve Demon Moons, remaining at that rank for hundreds of years, while his original name was lost to history.