Four knights of the apocalypse, 13

The group heads to the demon world. One of King Arthur's assassins has taken the life of a beloved comrade, but the knights overcome their grief and set out on their journey. It is then that, guided by the demon Io, who claims to know the location of a gate leading to Camelot, they arrive in the demon world. In this land of miasma, not only threats and hostility await them, but also an unexpected secret: Percival's hidden past!