Senyu. Specials Shitsujichou no Tabi Sono 1

In the story, a gigantic hole suddenly opened up in the world one day, and demons appeared. The king thinks that this portends the return of the demon king Rukimedesu, who was sealed away by the hero Kureashion a millenium ago. The king decreed that the descendants of the hero must take on the threat, and 75 people showed up. Hero No. 45 (Aruba) and a sadistic palace warrior (Ross) team up, and their adventure begins.