心を鬼にする

• Reading: こころをおににする
• Romaji: kokoro wo oni ni suru
• Kanji breakdown: 心 (shin/kokoro) — heart, mind; 鬼 (ki/oni) — demon, ogre
• Pronunciation: /ko̞.ko̞.ɾo̞ wo̞ o̞.ni ni sɯ.ɾɯ/

Meaning

To steel oneself; to harden one's heart; to be ruthlessly decisive for someone's own good. Forcing oneself to act severely despite compassion.

A fixed Japanese idiomatic expression (慣用句). Literally means 'to make one's heart into a demon/ogre.' Used when someone must take a difficult or painful action — such as enforcing rules, refusing help, or making a harsh decision — for the long-term benefit of another. Not malicious; it implies reluctant severity born of care rather than cruelty.

Examples

1. 心を鬼にして息子に一人暮らしをさせることにした。 Steeling herself, she decided to let her son live alone.
2. 彼女は心を鬼にして、友人の甘えを断った。 She hardened her heart and turned down a friend who was being too dependent on her.
3. 部長は心を鬼にして、成績不振の社員をプロジェクトから外した。 The department head steeled himself and removed an underperforming employee from the project.

Usage Guide

Context: parenting, management, decision-making, idioms

Tone: neutral

Origin & History

A classical Japanese idiomatic expression. The oni (鬼) of Japanese folklore is a fearsome, merciless demon, so 'making one's heart into an oni' evokes the act of suppressing natural tenderness to do what must be done.

Cultural Context

Era: Classical

Generation: All ages

Social background: Universal