Taking a hardhearted stance with 心を鬼にする
The expression 心を鬼にする means to make a difficult or harsh decision, often one that involves being stern, unsympathetic, or strict, especially in situations where kindness or leniency might be expected.
Literal Meaning
This expression literally translates as “to turn one’s heart into an ogre”.
Usage
The nuance behind this expression is that you are intentionally suppressing your compassionate or empathetic feelings in order to do something necessary but harsh, such as disciplining someone, making an unpopular decision, or enforcing rules without compromise. It implies a kind of emotional toughening, where you make a conscious effort to act in a way that might seem “cruel” or “unyielding” for a greater purpose or to maintain order.
For example, a parent might use this expression when they need to punish their child, even though it pains them to do so, or a leader might use it when they need to make a decision that will be difficult for others but is necessary for the greater good.
While the expression often refers to being hard on others for their benefit, it can equally apply to being strict or harsh with oneself for personal growth, achievement, or necessity. In this usage, it conveys the idea of suppressing one’s own desires, comforts, or emotions to pursue a challenging goal, make a tough decision, or do something necessary but personally painful. It reflects self-discipline or self-sacrifice, showing a resolve to overcome internal resistance or weakness. The nuance remains that the action involves emotional struggle and deliberate firmness.
Dictionary Definition
かわいそうだと思いながら、厳しい態度をとる。
To take a harsh attitude (with someone) while feeling sorry (for them).
Goo Dictionary
Further Reading
- 心を鬼にする|慣用句 (edewakaru.com)
Examples
Being strict about eating sweets with 心を鬼にする

Having gained weight recently, Mie asks Komura to stop her from eating sweets at school, a difficult task as it’s White Day.
Komura repeatedly stops Mie from eating the cookies and chocolate she’s received as gifts. His resolve weakens as he finds it adorable how Mie tries to sneak a bite whenever he’s not looking.
- 小村:
- 「で…でもダメだ! 三重さんが一度決めたことを破らせては… 心を鬼にしないと…!!」
- “But, that's no good! If I let Mie break her decision... I have to be strict for her sake!”
Being strict with oneself and one's student with 心を鬼にする

Conan’s classmates aren’t fond of their new teacher’s strict attitude. Ms. Kobayashi explains how at her last school, she couldn’t bring herself to be strict, and it allowed her students to get so out of control that students were injured in a fight.
- 小林:
- 「だから、この学校では二度とあんな事は繰り返すまいと…」
- “Therefore, to keep from repeating that kind of situation at this school...”
- 「心を鬼にして自分にも生徒にも厳しくしてきたの…」
- “I hardened my heart and became strict, with myself and with my students...”
Club training with 心を鬼にする

Renge wedges herself into the Ouran High School Host club, appointing herself the club’s manager. Due to her social status, Tamaki and the other wealthy club members are unable to object. Instead, they leave it to Haruhi to oust her.
- 環:
- 「これもホスト修行だハルヒ!!」
- “This, too, is host training, Haruhi!!”
- 「おとーさんは心を鬼ににするぞ!!」
- “Dad has to harden his heart!”