A team of researchers at the RIKEN Center in Japan has successfully constructed a digital model of a mouse's entire cerebral cortex, leveraging the immense computational power of the 'Fugaku' supercomputer. This sophisticated model incorporates 9 million physical neurons and 26 billion synapses, spanning across 86 distinct brain regions. It stands as the largest and most intricately detailed animal brain simulation system created to date. The paper detailing this breakthrough was accepted by SC25 on August 15, 2025, with a live demonstration slated for November 20 (local time). To achieve this feat, the research team engineered and fine-tuned a lightweight biophysical neuron simulator, specifically optimized for the 'Fugaku' supercomputer's architecture. This simulator boasts exceptional scalability, enabling it to seamlessly simulate the mouse cerebral cortex across all nodes of 'Fugaku'. The study convincingly shows that high-performance computing technology holds the key to constructing digital replicas of entire mammalian brains, thereby paving the way for future advancements in brain simulation research.