"Time" is beautiful, empty and cruel. Time cannot be reversed. But is that true?

Do you regret anything? Why don't you reverse time then and change what happened?

In Chronos Ruler, Koyuki—the main character—can no longer dance with her friends because she was injured after saving a child from a car accident. Watching them get ready for the show is so painful that she's tempted to go back in time and change what she's done. But is it really worth it? If you turn back time, no matter how regrettable it is, it can't be undone.