みるみる・見る見るmirumiru[1]atamadaka (head-high)

1. adverbvery fast; in a twinkle; before one's eyes
   オーナーたちは新あたらしいレストランのおかげで見る見みるみるうちに大金たいきんをかせいでいた。↗

   The new restaurant was making the owners money hand over fist.

• Synonym見る間にみるまにNeutralLike 「見る見る」, it describes something happening right before your eyes in a moment; 「見る見る」 often takes 「うちに」.
• RelatedたちまちNeutralMeans 'in an instant' or 'at once', without the sense of watching it happen; 「見る見る」 stresses seeing the change with your own eyes.
• AntonymゆっくりNeutralMeans 'slowly', the opposite of the rapid change 「見る見る」 describes.

Use 「見る見る（うちに）」 or 「見る間に」 for rapid change before your eyes; 「たちまち」 for 'in an instant' without that visual sense, and 「ゆっくり」 for slow change.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

1. 見みている間あいだに物事ものごとが急激きゅうげきに変化へんかするさま。