GRAMMAR DETAIL

だに

merely thinking of

Indicates that merely thinking about something, without actually experiencing it, evokes a strong emotion.

Examples

故郷を失った人々の心情は想像するだに胸が痛む。

My heart aches merely imagining how people who lost their hometowns must feel.

災害の夜を思うだに胸が苦しい。

My heart feels heavy merely thinking of the night of the disaster.

事故の瞬間を思い出すだに恐ろしくなる。

Merely recalling the moment of the accident fills me with fear.

Structure: Attach だに to a dictionary-form verb such as 思う or 想像する to express, in literary language, a strong emotion evoked merely by thinking or imagining.
Basic usage: 事故の瞬間を思い出すだに恐ろしくなる。 means becoming frightened merely by recalling the moment of the accident.

Expanding it with だけで
- 想像するだに胸が痛む means that imagining alone makes one's heart ache, as in 想像するだけで胸が痛む. The だに version is more literary and presents the emotional response emphatically.