They are able to fix things but at a high price. It turns out that each time she clones her stamina drops by a percentage. So her current limit at 12 bodies is because she's only at half of her maxim

Title: My Hero Academia: Duet of the Unyielding Spirits Chapter 1: Unscathed Harmony Misaki always stood out with her unique physique - two heads and four arms - born due to her quirk, "Duet." Life in UA was exhilarating for her. Her newfound ability to duplicate herself via a process paralleling cell mitosis earned her commendable glances and encouraging cheers. As her days in UA continued, another joyous event occurred - she found her match. Not just in the mundane sense, but in the world of quirks as well. Syouma, a boy who carried the aura of calmness around him despite his quirk “Impact Absorber,” gave her the comfort she needed. Their powers, as diverse as they were, synchronized as beautifully as a symphony. With Misaki's ability to duplicate and Syouma's protective power to absorb and release forces, they became a duo whose heroism was nigh unstoppable. One evening while they enjoyed their flighty teenage romance, a sudden commotion diverted their attention. It was a super villain unleashing chaos around them. Given the absence of pro-heroes on sight, they resolved to capitalize on their combined strengths. Chapter 2: Clashing Notes The villain was a wiry woman with an uncanny ability to control anyone she touches. Her power drastically shifted the balance on their initially unified front. Misaki, while brave, was unfortunately limited by her own quirk. With the villain managing to touch one of her duplicated bodies, she had wormed her way into invading the troupe Misaki controlled. The battle grew intense. Every time Misaki split to evade the villain, one of her bodies was turned against the next. The landscape changed from a chaotic street to a cataclysmic battlefield with Misaki's duplicates battling each other, leaving Syouma straining to absorb the relentless forces around them. Chapter 3: Unyielding Spirits Misaki, exhausted and losing focus from the abuse of her quirk, was growing desperate. Syouma, too, was fiercely absorbing impacts, but was faltering under the stress. Yet, their faith in each other and commitment to defeat the nemesis never wavered. All of a sudden, Misaki had an idea. She glanced at Syouma, signaling him to get ready. Then, she deliberately created a final duplicate, expending the last of her energy. As the villain reached out to control this new clone, Syouma, who had been siphoning all the force around him, released a powerful blast, just in time. The impact broke the villain’s control over Misaki's clones. Together, Misaki and Syouma subdued the villain, proving they were not just any high school couple, but a formidable team of heroes. Their tale of courage and unity echoed throughout the city, an inspiring duet sung by their harmoniously combined quirks. Yet, this encounter was only an overture to the melody of their hero journeys. They held hands; they knew more challenges awaited them, but together they were ready to face anything.