Sourpuss was a normal pony once, a pony who hated everything. With his trademark sour disposition he pushed everyone around him away. However when the war started he found a purpous with the Minestry of Morale.
After the war ended Sour couldn't let it go, so now he's creating reports on the apocalypse.
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Well I mean, the whole point of the story is that he's making reports.