User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-168.235.200.238-20150821153830/@comment-3965848-20150825174156

Issei and Kiba can't battle Vali and Arthur in a RG because none of Team Vali have any Evil Pieces or Brave Saints to take part in it, except for Kuroka but it's not like Vali is her King.

Their fight will just be on their on time and when it'll come or who comes out the winner is currently unknown at this point.