Demon Slayer: Kimetsu No Yaiba, the Genius Swordsman of the Uyashiki Family

[Demon Slayer fanfic, the protagonist doesn't know the plot and is semi-invincible] Evil spirits are rampant and all living beings are in ruins. Utsuya Shikifuzushima's family is from the same lineage as the ancestor's ghost, so they were punished by God, and none of their descendants were weak and could not live past the age of thirty. However, Fengyu escaped divine punishment. He was born with markings and a transparent world. In order that no one would be harmed by evil spirits, and in order to cut off the family's thousand-year karma, Fengyu joined the ghost killing team and vowed to end the evil ghosts.