Translation guide
The phrase 'at heart' describes someone's true, fundamental nature or deepest feelings, often in contrast to their outward appearance or behavior. It can also mean 'in essence' or 'basically' when describing the core character of a person or thing.
To express that someone is fundamentally a certain kind of person, despite appearances or actions.
Literally 'the root is', this is a very common and natural way to say someone is essentially a certain type of person. Often used with adjectives or nouns describing character.
He is a kind person at heart.
To describe the fundamental nature of something, not just a person. Similar to 'essentially' or 'basically'.
Do not translate 'at heart' literally as 心に (こころに) or 心で (こころで). These mean 'in the heart' as a location, not the idiomatic sense of true nature. Use the phrases above instead.
He's serious at heart, but he's always joking around.
Means 'in one's heart/mind', emphasizing inner feelings or thoughts that may not be shown outwardly.
At heart, I respect her.
Means 'actually' or 'in truth', often used to reveal someone's real nature or feelings.
He is actually a lonely person at heart.
Means 'originally' or 'by nature', used to describe inherent character. Slightly more formal or written.
He is a kind-hearted person at heart.
This plan is a good idea at heart.
He is an honest person at heart.
Means 'essentially' or 'in essence'. More formal and often used in analytical contexts.
At heart, this problem is a lack of communication.