When K-pop girl group AtHeart debuted in August 2025 with its first EP "Plot Twist," the title track captured the emotional swings of teenage life. Crushes felt mysterious, feelings were confusing and the members leaned into the carefree brightness of youth. Seven months later, the group says it has found something new — confidence. Returning with the paired singles "Shut Up," released Feb. 26, and "Butterfly Doors," set to follow Wednesday, AtHeart is presenting what the members describe as a more "self-assured side" of the group. The back-to-back releases mark the group's first comeback since its debut and form a connected story about growth. "When we debuted, all of us were teenagers, so the concept naturally reflected that youthful energy," member Arin said in an interview at The Korea Times office Monday. "This time, some of us have become adults, so we naturally wanted to show a more mature side. It feels like our atmosphere as a team has developed." The new era is also visually anchored by a symbol the group calls "The Black Heart." Ahead of its comeback campaign, AtHeart unveil