• 再会さいかい — reunion
• 再生さいせい — playback; regeneration
• 再開さいかい — reopening; resumption
• 再起さいき — recovery; comeback
• 再度さいど — again; once more
• 再利用さいりよう — reuse; recycling
• 再婚さいこん — remarriage
• 再試験さいしけん — retest

The character 再 signals repetition or a second occurrence. It’s highly productive as a prefix meaning “re-” in modern vocabulary, especially in digital/media contexts (e.g., 再生 “playback”) and scheduling (再開 “reopen/resume”).