Japanese by Example
Learning through examples in manga

Taking a hardhearted stance with 心を鬼にする

The expression (こころ)(おに)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(おも)いながら、(きび)しい態度(たいど)をとる。

To take a harsh attitude (with someone) while feeling sorry (for them).

Goo Dictionary

Further Reading

Examples

Being strict about eating sweets with 心を鬼にする

好きな子がめがねを忘れた » Volume 2 » Page 119

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(こむら):
「で…でもダメだ! 三重(みえ)さんが一度(いちど)()めたことを(やぶ)らせては… (こころ)(おに)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

名探偵コナン » Volume 16 » Page 91

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(こばやし):
「だから、この学校(がっこう)では二度(にど)とあんな(こと)()(かえ)すまいと…」
“Therefore, to keep from repeating that kind of situation at this school...”
(こころ)(おに)にして自分(じぶん)にも生徒(せいと)にも(きび)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

桜蘭高校ホスト部 » Volume 1 » Page 127

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.

(たまき):
「これもホスト修行(しゅぎょう)だハルヒ!!」
“This, too, is host training, Haruhi!!”
「おとーさんは(こころ)()ににするぞ!!」
“Dad has to harden his heart!”