Sharding alleviates the scalability bottleneck of blockchain systems by parallelizing transaction processing across multiple shards, but dispersing mining power lowers the security threshold of each individual shard, which typically requires additional mechanisms and overhead to restore. In this paper, we introduce Monosulfide, a PoW sharded blockchain that employs a braided-chain architecture to safely enable adaptive allocation of computational power across shards, while preserving both sharding and decentralization benefits. At its core is G-MOS, a novel pivot-graph confirmation algorithm that unifies local longest-chain mining with a global cumulative–work rule to provide lock-free parallel mining and robust fork-safety. We formalize the notion of mineable block sets and prove that G-MOS achieves security equivalent to a single canonical chain. Monosulfide allows miners to focus on hot shards with only minimal additional storage, achieving automatic load balancing. Our prototype demonstrates that, at the theoretical maximum transaction injection rate, Monosulfide delivers over 3x the throughput of Monoxide with 8 shards and over 6x with 16 shards, while maintaining low orphan rates and bounded confirmation latency under strong safety and liveness guarantees.