Okay, the user wants me to translate "lack of regret" into Japanese. Let me think about the right term here. "Lack of" would be something like 無し or 無い, but in this context, maybe 無い is better because it's more about absence. "Regret" is 后悔 (koukai). So putting it together, "lack of regret" could be 后悔の欠如. Wait, is there a more natural way to say it? Maybe 后悔がない, but that's more like "no regret." The original phrase is "lack of," which is a bit more formal. Alternatively, 后悔の欠如 is a direct translation. Let me check if that's commonly used. Hmm, maybe 后悔がない is more straightforward and natural in Japanese. But the user might prefer a direct translation. Let me confirm. The user's rules say to translate all content into Japanese, and if it's already in Japanese, leave it. So "lack of regret" is English, so I need to translate. The most accurate would be 后悔の欠如. But maybe the user wants a more natural expression. Alternatively, 遺憾の欠如 could be another option, but 遺憾 is more like "regret" in a formal sense. I think 后悔の欠如 is correct. I'll go with that.