Backend Engineer (AI/LLM) - Mercari Marketplace

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Backend Engineer (AI/LLM) - Mercari Marketplace

• Employment Status:　Full-time
• Work Hours: Full Flextime (no core time)
• Office: Roppongi

For more details, see the Overview of Our Positions section on our Careers site.

　
About Mercari

Circulate all forms of value to unleash the potential in all people

"What can I do to help society thrive with the finite resources we have?" The Mercari marketplace app was born in 2013 out of this thought by our founder Shintaro Yamada as he traveled the world. We believe that by circulating all forms of value, not just physical things and money, we can create opportunities for anyone to realize their dreams and contribute to society and the people around them. Mercari aims to use technology to connect people all over the world and create a world where anyone can unleash their potential. For more information about Mercari Group’s mission, see Mercari’s Culture Doc

　
Organization/Team Mission

Mercari Engineering Principles

Mercari Engineering Principles are a shared understanding that serves as the foundation of engineering beliefs and behavior at Mercari. The Engineering Principles are designed to complement the organizational identity (Mercari’s mission, values, and culture) from an engineering viewpoint.

These principles ultimately help us achieve Mercari’s mission by defining the ideal state we seek to realize in the long term.

• Passion For The Product
• Grow Together
• Solve Through Mechanisms
• Collaborate Openly

For more details, please see the following link:

• Engineering Culture

The AI / LLM Team’s mission is focused on two core pillars, "building" and "enabling", delivering new AI-driven features and user experiences to maximize product-facing impact for Mercari's business. We do this both through independent initiatives owned by our team, as well as by horizontally collaborating with product and engineering teams across the entire organization.

As a Backend Engineer on the AI/LLM team at Mercari, you will play a key role in designing, developing, and operating backend systems that support our cutting-edge AI and ML applications. You will work closely with ML researchers, data scientists, and other stakeholders to build robust, scalable, and efficient backend services that drive impactful AI-driven solutions for millions of users.

See here for more information about our mission and values.

　
Work Responsibilities

• Design and Develop Solutions: Design, develop, and optimize backend systems and APIs to support the integration and operation of AI/LLM models & MCP tools. Ensure these systems are robust, scalable, and efficient to handle large-scale production environments.
• Collaborate on Product Roadmaps: Work closely with product managers and business development teams to plan and execute the product roadmap for AI-driven features, ensuring alignment with business goals.
• Integrate with External Partners: Collaborate with external partners to understand their system limitations and design solutions that benefit both Mercari and its partners. Ensure smooth integration and operation of AI/LLM solutions with partner systems.
• Enhance Existing Features: Collaborate with internal teams to enhance existing features that depend on other teams across the organization. This may involve refactoring and optimizing existing codebases to improve performance and scalability.
• Develop and Maintain Infrastructure: Build and maintain the backend infrastructure required to support AI/LLM and MCP services, including data pipelines, deployment scripts, and monitoring systems.
• Testing and Quality Assurance: Develop and implement comprehensive testing strategies, including unit, functional, and end-to-end testing, to ensure the reliability and performance of backend systems.

　
Unique Challenges

• In this position, you will have the opportunity to work on innovative AI-driven products that leverage Mercari Group’s vast data assets, creating high-impact user experiences for tens of millions of users.
• You will face the unique challenge of managing the expectations of stakeholders and partners while ensuring that backend systems are robust and scalable enough to accommodate the expanding feature set and load.
• Work at the intersection of cutting-edge AI research and practical backend development, translating state-of-the-art AI/LLM developments into tangible business solutions.

　
Qualifications

• Required Experience/Skills
• Shared belief in the mission and values of Mercari Group and its various companies.
• 3+ years of experience working on large-scale backend systems.
• Experience with backend design, development, and operational skills considering the load of large-scale services.
• Ability to design and develop with performance and scalability in mind.
• Good communication and interpersonal skills with the ability to collaborate with multiple stakeholders.
• Knowledge and development experience in software testing, including unit testing, functional testing, and end-to-end testing.
• Knowledge and familiarity of modern infrastructure and observability technologies (Kubernetes, Terraform, DataDog)
• Knowledge and experience in data model design and queries to efficiently utilize databases (RDBMS, NoSQL).
• Development experience in the cloud, especially with GCP or AWS.
• Development experience in a team using Git/GitHub or similar version control systems.
• Basic understanding of ML concepts, including model inference, embeddings, and vector similarity search.
• Passion for the products and technologies.

• Preferred Experience/Skills
• Experience designing, developing, and operating APIs in Go & Python.
• Experience developing and operating with microservices architecture.
• Experience in on-call support of services.
• Experience in integrating development with third parties.
• Experience with AGILE methodology.
• Experience with working on agentic/MCP servers and tools.
• Experience deploying and operating ML models in production environments (e.g., model serving, versioning, A/B testing).
• Familiarity with vector databases or embedding pipelines (e.g., Pinecone, Weaviate, pgvector).
• Active participation in the open-source community.

• Language
• English: Independent (CEFR - B2) (required)
• Japanese: Independent (CEFR - B2) (optional)

For details about CEFR, see here.

　
Learn More About Mercari Group

• Careers site: https://careers.mercari.com/en/
• Mercan: https://mercan.mercari.com/en/
• Social media: X / Linkedin

　
Recruiting at Mercari

At Mercari Group, we value empathizing with and embodying the mission and values ​​of the Group and each company. To promote the creation of an organization that maximizes the total amount of value exhibited by all members, we would like to understand the experience and skills of each candidate as accurately as possible.

Recruiting cycle at Mercari Group

• Application screening
• Skill assessment: For engineering positions, you will be asked to complete a skill assessment on HackerRank or GitHub. For non-engineering positions, you may be asked to complete an assessment depending on the position. (The timing of the assessment may coincide with the interview process.)
• Interview: The number of interviews may vary depending on the position.
• Reference check: We will ask for online references around the timing of the final interview.
• Offer: Offers will be determined carefully in consideration of the final interview and the reference check.

　Learn more about our recruiting process here.

　
Equal Opportunity Hiring

Here at Mercari, we work to realize a world in which no one’s potential is limited by their background and everyone has the opportunity to freely create value. We also firmly believe that a mindset of Inclusion & Diversity is essential for us to achieve our mission.

This, of course, extends to our hiring practices as well. Mercari is committed to eliminating discrimination based on age, gender, sexual orientation, race, religion, physical disability, and other such factors so that anyone who shares our mission and values can join us, regardless of their background. For more details, please read our I&D statement.

Please read and acknowledge our Privacy Policy prior to submitting your application.