Haken Lead Java Engineer - E-commerce & REST API | Tokyo

Join one of Japan's leading e-commerce and online marketplace technology companies as a Lead Application Engineer (Java / Checkout Core), taking ownership of the architecture, reliability and ongoing development of mission-critical shopping cart and checkout systems.

Based in Tokyo, this contract opportunity offers the chance to lead technical initiatives supporting an online marketplace used by millions of shoppers and tens of thousands of merchants across Japan.

You will provide architectural leadership for core checkout services, shopping cart functionality and merchant-facing RESTful Web APIs, ensuring that essential transaction systems remain scalable, secure, reliable and responsive under heavy traffic.

The role requires extensive expertise in Java software engineering, system architecture, high-concurrency application design and production operations, together with the leadership capabilities needed to guide engineering teams through complex technical challenges.

A central responsibility will be overseeing the end-to-end architecture, basic design and operational excellence of critical e-commerce applications. You will help establish sound technical decisions that support both immediate delivery needs and long-term platform sustainability.

You will also lead the response to major production incidents, coordinating technical investigations, conducting root cause analysis and implementing preventative measures that reduce the risk of recurring failures.

Beyond hands-on engineering, you will translate executive-level organisational strategies into actionable technical roadmaps, development milestones and engineering priorities, aligning platform evolution with wider business objectives.

As a senior technical leader, you will champion continuous improvements in system quality, performance and reliability, particularly within high-traffic online marketplace environments where service stability directly affects customers and merchants.

You will also mentor engineers, delegate meaningful technical ownership and encourage independent decision-making, helping build capable and accountable engineering teams across distributed working environments.

This is an excellent opportunity for an experienced Java Technical Lead, Lead Backend Engineer, Java Architect, Principal Software Engineer or E-commerce Platform Engineer seeking to influence large-scale transaction systems and technical strategy.

Please note: This position is open only to candidates currently residing in Japan.

Key Responsibilities

• Lead the end-to-end architecture, basic design and technical development of core shopping cart, checkout and merchant-facing application services.
• Design, maintain and enhance RESTful Web APIs supporting mission-critical e-commerce and online marketplace operations.
• Provide architectural direction for high-traffic, high-concurrency Java applications, ensuring scalability, reliability and maintainability.
• Take technical ownership of production operations and service stability across essential transaction processing systems.
• Lead responses to major production incidents, coordinating troubleshooting, technical investigation and service recovery.
• Conduct comprehensive root cause analysis (RCA) and implement long-term corrective actions to prevent recurring system failures.
• Translate executive-level business and organisational strategies into practical technical roadmaps, delivery milestones and engineering priorities.
• Identify and communicate technical debt, architectural trade-offs and systemic risks to engineering leaders and business stakeholders.
• Drive continuous improvements in application quality, operational reliability, system performance and engineering processes.
• Collaborate with cross-functional and distributed engineering teams to coordinate technical decisions and delivery activities.
• Mentor engineers through delegated technical ownership, constructive guidance and opportunities for independent decision-making.
• Support the long-term evolution of large-scale e-commerce platforms, balancing immediate operational requirements with strategic modernisation goals.

Required Skills and Qualifications

Experience:

• 10+ years of professional Java software development experience.
• Deep understanding of the full Software Development Life Cycle (SDLC), from requirements and design through implementation, testing, deployment and production maintenance.
• Proven experience architecting, developing and maintaining RESTful Web APIs in large-scale production environments.
• Strong track record supporting high-traffic online platforms, with an understanding of scalability, high concurrency and application reliability.
• Extensive hands-on experience managing major production incidents, critical system failures and complex technical troubleshooting.
• Demonstrated ability to perform root cause analysis and implement long-term measures to improve system stability.
• Experience taking technical ownership of system architecture, application design and operational performance.
• Ability to translate broader business or organisational objectives into practical engineering priorities and technical delivery plans.
• Experience working with cross-functional engineering teams and coordinating technical decisions across multiple stakeholders.
• Current residence in Japan is required for this contract position.

Soft Skills:

• Strong technical leadership and mentoring capabilities, with the ability to guide experienced engineers and encourage independent ownership.
• Excellent executive-level communication skills, including the ability to explain technical debt, architectural trade-offs and system risks to business stakeholders.
• Ability to align day-to-day engineering realities with wider organisational strategy and management directives.
• Strong analytical thinking, structured problem-solving and decision-making skills under pressure.
• Collaborative leadership style combining clear technical direction with effective followership and stakeholder alignment.
• Proactive approach to continuous improvement, operational excellence and long-term platform reliability.
• Ability to work effectively with multicultural and distributed engineering teams.

Language Requirements:

• English: Business-level proficiency, approximately equivalent to TOEIC 800 or above, is required for leading technical discussions with internationally diverse engineering teams.
• Japanese: Conversational proficiency is indicated in the position details, supporting communication within the Japan-based working environment.

Preferred Skills & Qualifications

• Proven experience leading legacy system modernisation, architectural migrations or large-scale system redesigns.
• Experience delivering technical improvements within high-volume e-commerce platforms, online marketplaces or complex transaction processing systems.
• Hands-on familiarity with Java, Spring Framework and React within modern application development environments.
• Direct experience in engineering management or technical team leadership.
• Experience coordinating cross-departmental technical initiatives involving multiple engineering or business functions.
• Involvement in engineer evaluation, talent development and agile team building.
• Experience establishing technical direction and driving long-term architectural improvements across complex software platforms.

About the Company

Our client operates one of Japan's flagship online marketplaces, supporting multi-trillion-yen annual transaction volumes and connecting tens of thousands of merchants with millions of consumers.

The organisation plays a major role in Japan's digital commerce ecosystem, delivering the technology infrastructure required to support high-volume online shopping and transactional services.

Its engineering division is responsible for maintaining and evolving one of Asia's sophisticated e-commerce transaction platforms, where performance, reliability and scalable architecture are essential.

Engineering leaders work on complex technical challenges involving high-concurrency systems, mission-critical checkout services, large-scale APIs and platform modernisation.

The company promotes a vibrant, multicultural and technology-driven environment, bringing together engineering professionals with different technical backgrounds and international perspectives.

Its technology teams are encouraged to develop forward-looking architectural solutions, improve engineering standards and drive modernisation programmes that strengthen the long-term capabilities of the platform.

Joining this organisation provides the opportunity to contribute to technology systems operating at significant national scale, while influencing technical practices within Japan's wider digital economy.

Why You'll Love Working Here

• Lead engineering initiatives for one of Japan's largest online marketplace platforms.
• Work on checkout and shopping cart systems supporting millions of shoppers and tens of thousands of merchants.
• Gain experience with multi-trillion-yen annual transaction volumes and highly demanding production environments.
• Influence the architecture and technical direction of mission-critical Java applications and RESTful APIs.
• Solve complex challenges involving high concurrency, scalability, system resilience and operational reliability.
• Take ownership of major incident management, root cause analysis and long-term system improvements.
• Translate strategic business priorities into technical roadmaps and engineering execution plans.
• Mentor engineers and help shape a culture of technical ownership, autonomy and continuous improvement.
• Collaborate with multicultural and distributed engineering teams in an internationally connected technology environment.
• Contribute to platform modernisation and long-term architectural evolution within Japan's e-commerce sector.
• Enjoy complimentary daily meals at the company's employee food hall.
• Benefit from a flexible hybrid working arrangement to support work-life balance.
• Receive comprehensive statutory health, labour and employment insurance coverage.

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