User blog comment:B214/Volume 21 info & spoilers/@comment-26821288-20160130213951

Returning from a long trip. High School DxD Volume 21, please look forward to it. I've place more effort into this volume than usual. It's the final chapter of the fourth volume. To be released on March.

"It's the final chapter of the fourth volume."

Correction: "It's the final volume/chapter of the fourth story arc"

Although, I did notice that it's a rough translation, but still, it seems pretty nice, besides what I mentioned.