こととなると

Usage

An expression that describes how a person's attitude suddenly changes when talking about a certain topic

田中さんはアクション映画のこととなると、話が止まらなくなる When it comes to action movies, Mr. Tanaka can't stop talking

部長はいつも怖いが愛猫のことになると、優しくなる The manager is always scary, but he becomes gentle when it comes to his beloved cat