User blog comment:Crimson and Darkness/Shin DxD 4 discussion/@comment-26926813-20200209115622/@comment-32428013-20200211143817

Literally it's "Kingdom of the Decisive Battle and of Study Abroad". "In the Kingdom" could be there only if the title is "キングダムの決戦留学", but there is actually "決戦留学のキングダム". Ichei has his own style of creating titles. For example: "Gremory of the Graduation Ceremony" (V22), "Phoenix of the Battle School" (V2). Vergil's variant is just a peculiar adaptaion.