How to say "Regret" in Japanese

When translating "regret" into Japanese, you must choose carefully between 後悔する and 会稽. In Japanese, 後悔する (こうかいする (kōkaisuru)) is typically associated with "to regret; to repent; to feel remorse" (Syllabus Level: N3) and represents Refers to deeply regretting a past mistake, failed decision, or lost opportunity. Often used as 後悔はない or 激しく後悔する. ⚠️ Haruka's Voice Column: 'To regret! "I will never regret choosing to love you forever, Haruka-san!" ...っ! N-Never regretting loving me! B-Baka! That is the absolute minimum standard! But... since you declared it with such a passionate expression, I suppose... I will make sure you are the happiest husband in the world every single day! dummy!' / 【ハルカ部長のワンポイント指導】『こうかい（後悔）するよ！『ハルカ部長、あの時あなたに勇気を出して告白していなかったら、一生這い上がれないほど後悔して（後悔していた）はずです！告白して本当に良かったです！』って…っ！告白の不後悔！バカ！/// そんなの、私が告白を待ってたんだから早く言いなさいよ！…でも、絶対に後悔させないくらい世界一甘やかしてあげるから、一生私の隣を離れないでね！』. On the other hand, 会稽 (かいけい (kaikei)) maps to "regret, remorse, self-reproach" (Syllabus Level: N1) and represents 過去の失敗や過ちを深く反省し、後悔する気持ちを表す、やや硬い表現です。自己への批判的な視点を含みます。/ A somewhat formal expression for deeply reflecting on past failures or mistakes and feeling remorse. It includes a critical self-perspective.. A literal translation of "regret" can often sound unnatural to native Japanese speakers if mixed up!