TLDR: Dentsu, Dentsu Digital, SoftBank Corp., and SB Intuitions have initiated a joint research project to develop a generative AI specifically designed for Japanese copywriting. This collaboration aims to overcome the limitations of existing large language models in capturing the subtleties of the Japanese language, leveraging SB Intuitions’ ‘Sarashina’ LLM and SoftBank’s AI infrastructure.
A significant collaborative effort has been launched by leading Japanese entities Dentsu Inc., Dentsu Digital Inc., SoftBank Corp., and its subsidiary SB Intuitions Corp. to develop a generative artificial intelligence (AI) specialized in creating compelling Japanese advertising copy. The joint research initiative, which commenced in September 2025, seeks to address a critical challenge in the advertising industry: the difficulty of generating advertising copy that accurately reflects the unique linguistic nuances and cultural subtleties of the Japanese language using predominantly overseas-developed large language models (LLMs).
The project aims to produce AI-generated advertising copy that not only enhances expressive performance but also allows for richer creative outputs. This will be achieved by combining Dentsu and Dentsu Digital’s extensive expertise in copywriting and AI advertising solutions with SB Intuitions’ ‘Sarashina,’ a Japanese-language optimized LLM. ‘Sarashina’ is being developed from the ground up with a deep understanding of Japanese language, culture, and expression, and will run on SoftBank’s robust AI computing infrastructure.
Each participating company has a defined role within this ambitious undertaking. Dentsu will be responsible for evaluating the generated advertising copy, ensuring its quality and effectiveness. Dentsu Digital will provide the crucial training data necessary for the Japanese copywriting-specialized AI. SoftBank Corp. will supply the essential AI computing infrastructure, providing the backbone for the model’s development and operation. Finally, SB Intuitions will lead the development of the specialized Japanese copywriting AI model itself, focusing on refining ‘Sarashina’ through techniques such as Supervised Fine-Tuning (SFT) and Direct Preference Optimization (DPO using real advertising copy.
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The research extends beyond mere copywriting, with aspirations to apply the AI’s capabilities to broader advertising tasks. These include naming, narration, verbalization of ideas and concepts, and advancing marketing research and analysis. The goal is to equip the AI with the ability to adjust the strength of tone and adapt word choice to specific marketing objectives and target audiences, thereby supporting creators in expanding their ideas and producing more innovative expressions. This initiative marks a significant step towards fusing AI with human expertise, aiming to deliver enhanced value to businesses and society by integrating problem-finding skills, creativity, and unique marketing methodologies into AI solutions.
