Usage patterns
〈事〉は初回のみ〈thing/offer〉 applies only the first time
This campaign is valid only for the first time.
初回から〈動詞〉to do something starting from the first episode/round
He gave it his all right from the first round.
初回限定〈物〉a 〈item〉 available only with the first release/printing
This album comes with a first-edition-only bonus.