It's a science fiction short story, where the main character has just come back from a war at the end of time to settle down in his home town, when a bunch of mercenaries from that same war come and start trouble in the town.
He kills all of them, revealing at the same time that he is essentially a Space Marine equivalent; the story ends with him being called back to the front, as it were.
I think I read it in one of the Year's Best Science Fiction anthologies, but I'm not sure. Does anyone know where there is at least a nicely searchable database of titles to go through?
