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Mercari

Peer-to-peer mobile marketplace for secondhand goods

Product Engineer - Backend

Backend EngineeringConfirmed live in the last 24 hours
Full-timeMinato City, Tokyo, JapanNo salary listed

About the Job

Requirements

  • Experience developing and operating web applications or backend systems, approximately three or more years.
  • Experience developing, designing, or operating large-traffic systems or systems using large-scale distributed databases, including relational, NoSQL, or NewSQL databases.
  • Ability to design database schemas, model data efficiently, and write queries.
  • Experience operating or tuning web applications and knowledge of security.
  • Experience designing software architectures and selecting middleware.
  • Ability to work with stakeholders to clarify ambiguous problems and translate them into technical solutions.
  • Ability to use generative artificial intelligence in development workflows to improve personal efficiency and team productivity.
  • Ability to define ambiguous problems, take ownership, and drive development forward.
  • Ability to lead specification clarification and consensus-building, and own work through production release and subsequent operations.
  • Practical ability to use AI coding tools such as Claude Code, while evaluating, correcting, and integrating AI-generated output.
  • Ability to rapidly create prototypes and use working software to establish specifications.
  • Ability to make independent technical decisions across architecture, APIs, data, security, and operations, and explain trade-offs in a business context.
  • Ability to work across backend, frontend, iOS, Android, quality assurance, and adjacent disciplines, and independently ramp up in unfamiliar areas using AI and documentation.
  • Willingness to mentor and coach colleagues and motivation to contribute to organizational growth.
  • Japanese proficiency at Independent level (CEFR B2) is required.

Responsibilities

  • Lead specification definition and implementation by building working software early, observing its behavior, updating and finalizing specifications, and leading cross-platform implementation.
  • Lead quality, measurement, and release readiness by ensuring event, log, and dashboard designs support measurement and by designing quality standards and phased rollout plans.
  • Make independent technical design decisions on architecture, APIs, data, security, and operations, explaining trade-offs in business context.
  • As a Product Engineer, own fintech work end to end from specification through production release, collaborating closely with product managers and stakeholders to finalize specifications based on working prototypes, and autonomously leading quality, measurement, release, and operations.
  • Design, develop, and operate Go microservices and APIs.
  • Design interfaces between microservices using Protocol Buffers and gRPC.
  • Design architectures and select middleware based on application requirements.
  • Improve system reliability through microservice performance tuning, monitoring, and alert response.
  • Measure initiative effectiveness and improve services through quantitative and qualitative analysis of user behavior logs.
  • Design accurate and scalable systems for complex payment, credit, accounting, and identity-verification domains, including legal requirements and strict data consistency.
  • Build and operate shared payment infrastructure handling diverse payments, currencies, and crypto assets at high traffic and high security.
  • Develop credit and underwriting products, including credit products offered by Merpay.
  • Develop and operate internal systems supporting reconciliation, settlement, and accounting integration across the group.
  • Develop and operate shared identity-verification platforms while meeting regulatory and compliance requirements and supporting user convenience.
  • Enable the Payment & Customer Platform organization through shared libraries, test environments, continuous integration and delivery, and quality assurance capabilities.
  • Develop and operate shared merchant and partner platforms supporting merchant applications, screening, contracts, stores, brands, payments, and settlement information.
  • Develop and operate infrastructure connecting group financial services with banks and ATMs, enabling secure and stable movement of funds.
  • Design and operate reliable, secure architectures for high-volume financial and payment traffic.
  • Design reusable interfaces and data models for platforms shared across multiple products, supporting future features and payment methods.
  • Structure ambiguous technical and domain problems, including distributed transactions, accounting, credit, and regulatory compliance, and work with the team to determine technical solutions.
  • Lead design and implementation of systems that maintain consistency in distributed transactions, support multiple currencies and crypto assets, and tolerate failures when integrating external payment providers.
  • Build accounting infrastructure that accurately reconciles large volumes of transaction and payment data, automate data processing, apply AI, and modernize legacy operations.
  • Modernize identity-verification systems, including large-scale data migration and new technology integration, without interrupting operations.
  • Lead development of shared financial-platform foundations and cross-team improvements to product delivery processes.
  • Design merchant-domain models and shared platforms, rearchitecting large live systems without interruption and accelerating new payment and financial services.
  • Develop critical bank and ATM integrations, maintain transaction consistency and idempotency, safely recover from failures, and evolve financial infrastructure without service interruption.

Desired Qualifications

  • Experience developing and operating with Go and Google Cloud technologies such as Kubernetes, Spanner, and Terraform.
  • Engineering experience in payment platforms, credit and underwriting, accounting and settlement, identity verification, anti-money-laundering and counter-terrorist-financing, or other domains with strict data consistency, accuracy, and regulatory-compliance requirements.
  • Experience leading technical-debt reduction, rearchitecture, or phased migration or replacement of legacy systems.
  • Experience leading developers or managing technical work, improving the technical capabilities of engineers or teams through design reviews and mentoring, and improving development processes.
  • Experience launching new services or scaling systems during rapid service growth.
  • Experience designing or operating large-scale data processing, batch processing, or event-driven architectures, and experience with data platforms or data integration using BigQuery or Dataflow.
  • Experience designing or operating systems that account for internal controls, audits, J-SOX, ISMS, SOC 2, or other security and non-functional requirements.
  • Experience in data analysis based on statistical methods.
  • Experience taking ambiguous specifications, building prototypes, revising and finalizing specifications, and delivering the result.
  • Experience designing measurement through events and logs, building dashboards, conducting phased rollouts, and making release decisions.
  • Experience working alongside product managers to finalize specifications and resolve decision-making delays.
  • Professional experience using English or developing products with multinational teams; English proficiency at Independent level (CEFR B1–B2) is welcomed.

About the Company

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Mercari

Peer-to-peer mobile marketplace for secondhand goods

Mercari operates a mobile peer-to-peer marketplace for buying and selling secondhand goods. Users list items by taking photos in the app, and buyers complete purchases there, with payments held in escrow until receipt is confirmed. Revenue comes from seller fees (10% in Japan; 10% plus 3.6% buyer protection in the US), plus Merpay payments and promoted listings, plus shipping partnerships for integrated delivery. The platform differentiates itself through a simple mobile experience, escrow and buyer protection, shipping integration, and a broader marketplace including Mercari Shops for sellers, with a goal of extending product life and supporting a circular economy.

Company size
1,001-5,000
Company stage
IPO
Headquarters
Tokyo, Japan
Founded
2013

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