Sometimes when the main story doesn't have enough chapters to make a full volume, they add oneshots at the end. It's not supposed to be in the middle of the story, so it's probably an upload error
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solstice258
undeed
So it could be, for example, that the one shot is placed at the end of volume 3 of a total story of 5 volumes.
... of the volume.
So it could be, for example, that the one shot is placed at the end of volume 3 of a total story of 5 volumes.