"Kono Subarashii Sekai ni Shukufuku wo!" (bless this wonderful world!) volume 15 by Akatsuki Natsume. Kazuma single-handedly defeats a demon lord's henchman in this volume.
This series is founded on having a party that is balanced in a strange way -- the offense, defense, and support roles are filled by Megumin, Dakness, and Aqua respectively. Kazuma doesn't seem to contribute materially to this balance, as he realized early on in this volume that all the past victories are mostly settled by other party members, often with explosions. But Kazuma must deal with the enemy alone this time and demonstrate his worth.
Kazuma came up victorious as we might expect, and he managed to win almost entirely through persistent harassment against the dark priest. Kazuma's role might have been the brains of his party, but his real contribution is the willingness to fight dirty every time. This is the real balance to the wholesome Konosuba: everyone is equally flawed.
There were many references to the first volume this time, as a constant reminder to readers that there is still a demon lord out there that is waiting to be defeated. Aqua has gained a lot more respect throughout this volume despite not having done much, and she has motivated the party to continue on with the original quest. The end might be near for this series.
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