Two Halves of the Same Whole.
Sunspark was born an identical twin; brother to Skyflare. His mother was a clan cat; a white-furred Windclan warrior named Cloudspirit. It was unknown to anyone who their father was, or whether he even knew of his kits existence. It was assumed to be a one-time fling and the topic was never broached. Cloudspirit was an unremarkable cat and a mild mother. As perfectly adequate a mother as any kit could hope for. Their relationship was strong, particularly between their mother and Skykit. Life in general seemed to be going well.
Sunspark and Skyflare had always been the rambunctious sort of children. On their own, they were as pleasant as any other kits. But whenever they shared the same space, chaos ensued. Cloudspirit had her work cut out for her trying to control her children. She tried her best at first, but was eventually pressed to give up and let them have free reign over the nursery, much to the dismay of other queens and kits. Having quickly grown bored with agitating the other kits, it wasn't long before they found their way out of the nursery and into the camp. And soon after that, the territory. When the adults weren't looking, little Sunkit and Skykit liked to have 'adventures' in the outskirts of camp and push the limits of how far they could wander without being noticed.
During one of their adventures, Sunkit stumbled upon a freshly dead field mouse, completely unscathed and still warm. Skykit enthusiastically suggested they pull a prank on the other kits by bringing it back to camp and claiming they caught it themselves. Sunkit pointed out that this would also be admitting that they had been wandering outside of camp, but Skykit dismissed it by calling him a scaredy-mouse. Sunkit didn't want to be a scaredy-mouse of course, so he half-heartedly played along with his sister's 'prank'. They carried the mouse back to the nursery and proudly showed off, retelling the dramatic, fantastical (and obviously fake) tale of their first catch, which of course, Skykit took most of the credit for. Unsurprisingly, the other kits were not impressed. Disappointed that their latest prank had fallen flat, the twins retired to their nest, bringing the mouse to their mother for her to eat.
The twins very quickly realized that they had made a tragic mistake. Within minutes of taking her first bite, Cloudspirit had collapsed and was convulsing on the ground. By the time help arrived, it was already too late. Cloudspirit had been poisoned. It was presumed that the mouse had eaten death berries, which killed it before they had time to be digested. In eating the mouse, their mother had also become a victim of the death berries toxin. The death of their mother had profound and long lasting trauma on both of the kits, but none more than Skykit. For moons after her passing, Skykit was completely mute, refusing to speak even to her own brother. Perhaps she blamed herself for the accident. Whatever the reason, Sunkit quickly replaced Cloudspirit as a motherly figure for Skykit, who could do very little for herself.
However, something changed in his sister once again the day they were set to become apprentices. Be it the result of some sort of inner awakening, or simply being forced out of old habits, Skykit- now Skypaw- became almost unrecognizable to the quiet, despondent kit she'd been before. Driven by a fiery, almost frightening ambition, his sister was now the more dominant of the twins and almost completely eclipsed Sunpaw by comparison, who was glad to let himself be pushed around.