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arriving first
先着百名様に記念品を差し上げます。
We will give commemorative gifts to the first 100 people.
先着順で座席が決まるシステムだ。
It's a system where seats are determined on a first-come basis.
先着五名限定の特別セールを開催する。
We're holding a special sale limited to the first 5 arrivals.