Blood Child saw that Devil Marquises flew in his direction, and the six of them got together before getting near him. Now that there was a significant threat looming over their heads and they found out their Dukes sold them out, none of them cared about their previous rivalry.
The ability to become allies with those you considered enemies just a few hours ago was one of the advantages of devils' pragmatic mind.
The six Devil Marquises maintained a distance of one thousand meters from Blood Child. Although the red fog hindered their vision, they had ways to detect his presence after deducting his location due to that shout from earlier.
Soon after the Devil Marquises had gathered, the Devil Counts began to arrive.
Fifteen hours after Blood Child's summoning, all the Devil Lords that remained alive had assembled, and only then did they approach him.