Backend Engineer · Big Data Group / Backend Team → xfunction Team
Backend engineer in the Big Data Group for an e-commerce platform, initially on the backend team and later on the xfunction team. Developed and maintained systems with Golang, NextJS, ScyllaDB, k9s, ArgoCD, Kafka, and Spark in a Scrum environment. Played a central role as a founding member of the xfunction team. Previously, communication between the FE and BE teams and coordination with other departments was fragmented, causing significant delays — for example, a project scheduled for a June release slipped to October. For the new team, prioritized psychological safety through Drucker-style exercises, proactive communication among members, and expectation alignment with PdM and stakeholders, eliminating unintended project delays to zero within five months of the team's launch. Worked closely with designers and across departments and teams as a lead within the xfunction team. Built the data platform on Iceberg (Parquet storage) with Trino as the analytics query engine; leveraged AI to scrutinize the code and introduced Spark SQL's `CREATE OR REPLACE TABLE` syntax in the ingestion pipeline, improving processing speed and cost by 30%. Drove AI adoption by optimizing Claude Code's Agents (subagents) and harness — designed and rolled out a subagent setup that routes tasks to Opus, Sonnet, or Haiku by workload, cutting token usage cost by 50%.
Led development of an app and backend infrastructure for an Okinawa theme park business. Managed a team of 16 Vietnamese developers through English communication, including onsite collaboration in Vietnam (business trip and stay). Delivered IaC-based web infrastructure setup and release within 2 weeks of joining the project. Caught up with existing tech stack, configured DNS, built dev/stg environments, implemented release and monitoring to handle peak traffic of 1500 RPS. Implemented using PayloadCMS, SSTv3, and NextJS with REST API architecture. Designed a microservices-oriented architecture with service separation to distribute traffic spikes, with app backend handling 3000 RPS at origin. Built data analytics platform with Parquet format using Athena, Lambda, Glue, and Quick Suite (AWS), leveraging IaC and AI. Rapidly delivered native app development, backend construction, and admin panel implementation. Implemented an illustrated map feature that splits images and aligns them with coordinates. Faced tight deadlines and, as a tech lead, actively engaged with customers not only on technical aspects but also on business matters, providing proactive communication. When requirements expanded significantly beyond the initial scope, proposed AI integration to the customer as an alternative to team expansion, which became the company's first AI integration initiative using Devin. Reduced infrastructure costs by 30% through AWS serverless architecture, Savings Plans consultation with AWS, and Redis implementation to reduce RDS and Lambda cold start times. Built infrastructure as code (IaC) to create an AI-friendly environment from the start.
Web app development for a service that converts Furusato tax points into stock rights. Microservices architecture with overall traffic exceeding 20,000 RPS; the owned area handled up to 1,500 RPS. Implemented with Next.js 15 (App Directory) and GCP Cloud Run, with frontend performance tuning such as WebP/AVIF image optimization and lazy loading.
NextJS · GCP · Cloud Run
2024.04 — 2024.11
Monstarlab
Tech Lead · Contract Development
As a tech lead, managed a team of three developers and three QAs. Proposed migrating a system costing around 250,000 yen per month to one costing around 10,000 yen per month using Lambda and CloudFront. Also reduced the monthly operating cost — initially estimated at 1.5 million yen in pre-sales — through system optimization. To avoid dependency on specific individuals, introduced IaC and eliminated manual migration by writing everything in Golang. For the frontend, architected an ISR-like configuration with Astro JS to address SEO and display speed. While teams are typically staffed with single-role FE, BE, and infrastructure engineers, was assigned to the project as a full-stack engineer capable of handling the entire scope.
Worked on updating a corporate website. Collaborated with an overseas team and handled backend, frontend, and infrastructure as a full-stack engineer. Coordinated development with a team in Bangladesh, working asynchronously across time zones and holding meetings and specifications explanations as needed.
Golang · Vue3 · Nuxt3 · MySQL · AWS · HubSpot
2021.05 — 2022.07
KiteRa
Full-Stack Engineer · Regulation Management SaaS Development
Developed the backend in Golang and communicated with the frontend via JSON-RPC. A fast-paced development environment. Led the implementation of Japan's first electronic application system for the 36 Agreement via e-Gov.
Golang · Svelte · PostgreSQL · AWS
2020.09 — 2021.04
Fignny
CRM Software Development · CRM Service Development
Responsible for adding new features, fixing bugs, providing APIs, and defining items using NoSQL. Also handled document creation and debugging environment setup.
Scraping for Summary Sites · Data Scraping for Summary Sites
Implemented scraping with BeautifulSoup4 in two weeks. Introduced parallel processing with Celery and ThredPoolExecutor, and distributed processing on 20 EC2 instances.
Data Migration and Batch Processing Development · Data Migration and Analysis
Loaded various data sources with Alteryx and integrated them into SQL Server. Implemented parallel processing, data anonymization, and batch processing.
Alteryx · SQL Server · Windows Server · Batch Script · Python(Django) · Jira
2018.12 — 2019.02
SysNavi
Web Application Development - Budget Management Software Creation · Project for Visualizing Plans and Actuals
Combined markup data with ASP.Net logic. Responsible for user interface, admin interface, and backend logic.
ASP.NET C# · SQL Server · Bootstrap4 · HTML · JavaScript
2018.04 — 2018.09
Independent Business Owner
Import and Sale of Raw Ham · Import and Sale of Raw Ham
Aimed to import and sell raw ham from Spain, conducting supplier negotiations, farm visits, bacterial inspections, and customs clearance procedures. Acquired a food sanitation manager qualification. The project was suspended during fundraising.
Import · Food Sanitation Law
2016.11 — 2018.03
Sumitomo Chemical
Research and Development/RD-2016 · Development of Medical Grade Polypropylene Materials
Development of medical-grade polypropylene materials. Focused on suppressing injection molding distortion and developing materials to prevent contamination from UV exposure.
Polypropylene · Medical Grade
2015.06 — 2016.10
Sumitomo Chemical
Research and Development/RD-2015 · Battery Separator Material Development
Explored PP-based separator film materials. Focused on heat resistance, puncture strength, and porosity.
Polypropylene · Separator
2012.04 — 2015.05
Sumitomo Chemical
Research and Development Support/RD-support · Material Development Support for Packaging Materials
Assisted in the research and development of polypropylene films at Sumitomo Chemical's petrochemical research institute. Supported the development of packaging materials and battery separators.