Being strict about eating sweets with 心を鬼にする

Idiom Explanation: Taking a hardhearted stance 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(こむら):: 「で…でもダメだ！三重(みえ)さんが一度(いちど)決(き)めたことを破(やぶ)らせては… 心(こころ)を鬼(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!”; Literal: “B-but no! If I let Mie break what she decided once... I have to make my heart a demon...!!”

Key Points

1心(こころ)を鬼(おに)にする = “harden your heart and be strict, even if it feels cruel”

Here Komura means he has to stop Mie from eating sweets even though he feels bad for her.
The idiom often carries the nuance of being severe because you think it is necessary or ultimately good for the other person.

2鬼(おに) adds the image of acting harshly on purpose

The point is not that he literally becomes a demon, but that he must shut off his softness and act tougher than he wants to.
That matches the English “be strict for her sake” more closely than a flat “be mean”.

3〜ないと = “have to” in casual speech

「心(こころ)を鬼(おに)にしないと」 is short for a fuller “If I don’t harden my heart, that won’t work.”
In natural English here, it comes across as “I have to be strict.”

4The earlier clause explains why he feels forced into this stance

「三重(みえ)さんが一度(いちど) 決(き)めたことを破(やぶ)らせては…」 means “I can’t let Mie break a decision she made.”
That makes the idiom sound like reluctant resolve: he is talking himself into doing the hard thing.

さん is an honorific suffix attached to a person’s name to show respect and social distance, roughly equivalent to “Mr.”, “Ms.”, or “Mrs.” in English, though it’s used far more broadly and doesn’t specify gender or marital status.

Being strict about eating sweets with 心を鬼にする

Key Points

See Also