DZSA-02-Senior Software Engineer - Search

LegalOn Technologies is a global leader in legal AI solutions, trusted by more than 8,000 companies and law firms worldwide. The company empowers legal teams to review and negotiate contracts faster, with greater accuracy and confidence. Operating across Japan, the United States, and Europe, LegalOn is the first AI company from Japan to surpass ¥10 billion in annual recurring revenue (ARR) and has raised over $200M from leading investors including SoftBank and Goldman Sachs. It also has one of the largest and most global AI teams of any startups in Japan. In 2025, LegalOn achieved its first M&A by welcoming Germany's Fides Technology into the group, further accelerating global expansion. LegalOn combines LLMs, intelligent Agents and intelligent AI-driven workflows. Beyond legal, the company now offers specialized AI solutions including "CorporateOn," "CXOn," and "DealOn" to support diverse business domains requiring high expertise. In partnership with OpenAI, the company is redefining the legal AI landscape and developing innovative solutions for the future of professional work.

For more details about our company, products, and development organization:
https://legalforce-recruit.notion.site/LegalOn-Technologies-Candidate-Handbook-17d82a58637480d2836ae138e5b5ee95

Key Responsibilities

LegalOn Technologies is a leading company in AI product development, and our search and recommendation platform is one of the most important, mission-critical systems behind the products we deliver.
In particular, as search has become increasingly essential in recent years as a key enabling technology that expands the capabilities of LLM-powered applications, we are looking for a Senior Software Engineer who has a strong passion for technologies in this domain and is well-versed in software engineering.

In this role, as a Senior Software Engineer, you will take significant responsibility for designing, developing, and improving how search and recommendation features are integrated into our products. You will develop a deep understanding of how users leverage these capabilities within the product experience, and proactively take ownership not only of search and recommendation but also of broader product development. You will solve complex challenges to deliver the best possible experience for our users.

What Mission and Challenges You’ll Take On

• Collaborate with product managers to explore what exciting features we would deliver to our customers, understanding how search and recommendation capabilities fit into the broader product experience, make a practical plan about how the work should be done, and take responsibility for the delivery.
• Contribute to product development beyond search and recommendation when needed, applying your engineering expertise to improve the overall user experience.
• Mentor team members to help design software systems in sustainable/maintainable ways.

What You’ll Do

• Design, build, and deliver a wide range of search, recommendation, and Agent features/APIs.
• Enhance functionalities such as integrating LLM-powered applications with search/recommendation features.
• Proactively maintain and operate search and recommendation features/APIs.
• Collaborate with team members and other teams to investigate performance and accuracy issues in search, recommendation, and Agent systems in production environments, establish quantitative evaluation metrics, and drive improvements.
• Develop a deep understanding of how users interact with search and recommendation features within the product, and contribute to adjacent product areas to ensure a cohesive user experience.

• 5+ years experience in software engineering.
• Hands-on experience in developing or operating search systems (full-text search engines, search APIs, indexing pipelines, etc.)
• Experience developing web applications or data processing platforms using Python.
• A proactive attitude toward adopting AI-powered development processes and tools, regardless of prior experience.
• Knowledge of data structures and algorithms.
• Hands-on expertise in building highly reliable and performant web backend systems.
• Hands-on experience with one of the Cloud Infrastructure Services: AWS, GCP, or Azure.
• Ability to communicate in Japanese(JLPT N2 or compatible experience)

• MS or Ph.D. degrees in Computer Science, Mathematics, or other technology-related majors.
• Hands-on experience in Apache Lucene, Elasticsearch, or Solr.
• Hands-on experience in developing Agent applications and related component technologies such as LangChain, Ragas, LlamaIndex, etc.
• Hands-on experience in machine learning and natural language processing.
• Experience mentoring/training junior engineers.
• Leadership experience in large-scale projects or teams (10+ members) with a proven track record of delivering results
• A proactive attitude towards learning and adopting new technologies, including AI-powered efficient development and task execution
• Strong communication skills, with the ability to work effectively across diverse cultures in both English and Japanese
• Experience contributing to product features across multiple domains or technology areas, beyond a single specialization

• Proactively identify team and product challenges, take autonomous action toward solutions, and see them through to completion with full accountability
• Share expertise generously to help maximize the overall output of the team
• Collaborate effectively within and beyond the team, leading constructive discussions and sound decisions
• Think beyond your area of specialization — stay curious about how users experience the product as a whole and proactively broaden your domain knowledge