"Kono Subarashii Sekai ni Shukufuku wo!" (bless this wonderful world!) volume 17 by Akatsuki Natsume. The end is filled with explosions.
This volume is indeed the ending to the series! Having defeated all henchmen, Kazuma's party went on the final siege against the demon lord's castle. This was accomplished not via any clever tactics, but pure brute force application of no fewer than 36 explosions. It was a condensed show of the best bits of volume 9. It was climax right from the start.
Having breached the castle and reunited with Aqua, the party could have returned home and planned for a more leisurely attack, but Kazuma was persuaded to take on the demon lord by himself in a one-on-one fight. This is a very orthodox kind ending where the main hero defeats the final boss to complete the story, but of course what's orthodox everywhere else is quite unusual for this series. What is consistent for this series is all the dirty tricks that Kazuma pulled off to accomplish this feat, although his final finishing move was rather honorable.
The main story can be considered complete with the defeat of the demon lord, but there are still many holes to be filled, including some new holes that were opened in this final volume. Personally I am fine with the author not dragging on to exhaustively plug any hole, and leaving things a bit open at the end.
This has been a very satisfying and well balanced series, one that definitely managed to stand out among the very saturated scene of isekai novels. Highly recommended for anyone looking for comic relief in a slightly unconventional fantasy series.
Previous (2020-12-03): Cup Noodle model
Next (2020-12-20): "Kono Subarashii Sekai ni Shukufuku wo!" series by Akatsuki Natsume