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theakrista.dev
Thea Krista Casupanan

About

I’m Thea, a senior full-stack engineer based in Japan, with 15 years of building software across e-commerce, insurance, banking, fintech, real estate, and travel.

These days I split my time between two companies. At a travel-tech startup I lead an eSIM commerce platform and the backend of a new online travel agency. At a real-estate company I built and run a property marketplace end to end, building production AI systems with the Claude API along the way. On the side I run nihongojouzu.jp, a Japanese-learning PWA, because studying for the JLPT deserved better tools.

I’m now looking for a full-time tech-lead or senior engineering role where I can keep building and own the technical direction with a team. I also take on select consulting work alongside it.

How I lead

I lead from the code, not just the roadmap.

For the past few years I have been the final reviewer on every production release and the engineer founders bring problems to. Earlier, at a global insurance group, I led a Java Community of Practice and spoke at the company’s global engineering summit in Cologne on the inclusion of women in IT. Leading, for me, has never meant leaving the editor.

Final reviewer for production releases

I own the last sign-off before anything ships, and I established the staging-to-production release process the team now follows.

Onboarding and mentoring

I onboarded and now mentor the first engineer to join me, the first step from a one-person operation toward a team, and I remain the final reviewer for every production release.

Standards the team adopted

My reusable adapter patterns and query-optimization guidelines became the team's standard for new work, and I brought AI-assisted review into the pull-request flow.

Engineering's voice to the business

I work directly with CEOs, marketing, design, and UI/UX, turning technical trade-offs into decisions non-engineers can confidently make.

My journey

I grew up in a small province in the Philippines, where I studied Computer Science at a local university. Looking back, I don’t think I chose software engineering because it was a practical career. I simply enjoyed being around computers.

University life was simple and fun. My classmates and I spent countless hours playing DOTA over a LAN network we built ourselves. We learned how to assemble computers, configure networks, and even found creative ways to hide our games whenever a teacher walked by. Those moments sparked my curiosity about how computers worked and made learning feel like play. Math and logic always came naturally to me, so studying computer science never felt like an obligation, it felt like a hobby that slowly became my profession.

My first job was with a Japanese software company. I knew the fundamentals, but I quickly realized that building software for real users was very different from writing code in school. That experience became my real education: frontend, backend, databases, testing, documentation, automation, every project taught me something new. Over the years I worked across banking, fintech, insurance, e-commerce, real estate, travel, and SaaS, and each role expanded my perspective. Every move helped shape the engineer I am today.

One thing never changed: I love building software.

Many engineers move into management and leave the code behind. I took a different path: I lead from the code. For me that means owning the architecture, mentoring the engineers around me, and being the technical voice in the room with founders and stakeholders, while still designing systems and shipping them myself. Staying hands-on is not a step back from leadership; it is how I lead. Even after 15 years, opening my editor and building something new is still exciting.

Today, building software means understanding the entire product to me. I think about architecture, user experience, performance, infrastructure, DevOps, analytics, SEO, and how every technical decision affects the people using the product. Creating something end to end has become one of the most rewarding parts of my work.

The rise of AI has made engineering even more exciting. It lets us build faster, explore ideas more quickly, and spend more time on meaningful problems. I don’t see AI as a replacement for engineers, it’s a tool that amplifies what we can already do. We’re still the ones asking the questions, making the decisions, and taking responsibility for the outcome. Like every new tool, it comes with opportunities and challenges; the important part is learning to use it thoughtfully to build better products and solve real problems.

15 years after writing my first lines of code, I still feel the same excitement I did back in that university computer lab. That’s probably the clearest sign that I chose the right career.

Experience

Company names are generalized here for privacy. The full resume, with the real names and specifics, is available on request.

  1. Nov 2025 - Present

    Senior Full Stack DevOps Engineer · eSIM & Travel Startup (Tokyo)

    Full-time · sole engineer for six months, then onboarded and now mentor the first hire

    • Own end-to-end architecture and releases for an eSIM commerce platform (checkout, payments, automated QR fulfillment, cross-domain auth) as final reviewer for all production releases
    • Led backend architecture and partner API integrations for a new online travel agency product, designing reusable adapter patterns and query-optimization guidelines adopted by the team
    • Built a competitor price-monitoring system with automated Slack alerts that replaced manual market research
    • Onboarded and mentored a new engineer; introduced AI-assisted code review into the pull-request workflow

    Impact · Kept uptime, release schedules, and feature delivery through six months as the company's only engineer; established the staging-to-production release process used by the team

    Next.jsReactTypeScriptNode.jsExpressMongoDBVercelRenderSlack API

  2. Nov 2025 - Present

    Senior Full Stack DevOps Engineer · Real-Estate Marketplace (Tokyo)

    Concurrent role, built and launched the platform end to end

    • Built and launched a real estate viewing platform working directly with the CEO, marketing, design, and UI/UX teams
    • Resolved server-side rendering bottlenecks and added Lighthouse CI checks to the pipeline; built an audit-logged admin console and automated lead triage with agents, photographers, and SEO specialists
    • Built a Claude-powered property data ingestion pipeline that scrapes listings, extracts 図面 floor-plan data, validates it, and uploads results automatically
    • Built an AI inquiry-automation service (FastAPI + Claude) that classifies leads from email, Meta ads, and walk-ins, assigns agents via round-robin with Slack approval, and syncs to Pipedrive CRM
    • Manage domains and DNS for all company web properties

    Impact · Cut infrastructure costs 80% across Vercel, Render, and API usage; found a leaked API key costing ¥100k/month in unauthorized usage

    Next.jsTypeScriptNode.jsPythonFastAPIPostgreSQLVercelRenderClaude APISlack API

  3. Oct 2023 - Jul 2025

    Senior Backend Engineer · Global E-Commerce Marketplace (Tokyo)

    Contract · large-scale marketplace serving millions of users

    • Migrated PHP and GraphQL projects to Java REST APIs, cutting latency by 30%
    • Designed a Backend-for-Frontend application, reducing cross-team dependencies by 40%
    • Fixed and remediated security vulnerabilities across the marketplace; authored system designs and development specifications
    • Migrated legacy on-premise servers to the company's cloud with automated provisioning, containerization, and CI/CD pipelines

    Impact · Faster feature delivery through the BFF; reliable scalability under high load after refactoring and performance optimization

    JavaREST APIsPHPGraphQLCloud MigrationCI/CD

  4. Aug 2020 - Oct 2023

    Senior Software Engineer · Global Insurance Group (Tokyo)

    Life-insurance platform engineering

    • Designed and developed REST APIs with Spring Boot, Redis, Docker, and MySQL; built UI features with React and TypeScript
    • Deployed microservices on OpenShift and built serverless functionality with AWS Lambda
    • Managed vendors, reviewed PRs, remediated security vulnerabilities and technical debt, optimized SQL performance
    • Established logging-strategy practices for Node.js and Spring Boot applications

    Impact · Led the Java Community of Practice; spoke at the company's global engineering summit in Cologne on the inclusion of women in IT

    JavaSpring BootRedisMySQLReactTypeScriptOpenShiftAWS Lambda

  5. Mar 2019 - Jul 2020

    Front-End Engineer · Global E-Commerce Marketplace (Tokyo)

    Contract · item-page renewal for a marketplace serving millions

    • Delivered new features for the item-page renewal using React, Redux, and Node.js
    • Built components from Figma designs; implemented meta-tag SEO for the renewal application
    • Configured the marketplace's analytics tracker for A/B testing
    ReactReduxNode.jsSEOA/B testing

  6. May 2018 - Feb 2019

    Full Stack Engineer · Fintech Startup (Tokyo)

    Digital currency exchange

    • Designed and built social login and document-verification APIs with Spring MVC OAuth2
    • Modeled the Cassandra database; developed the exchange application front end
    ReactReduxSpring MVCOAuth2CassandraRedis

  7. Oct 2016 - Mar 2018

    IT Engineer · R&D Contracts (Japan)

    Projects for major automotive and electronics manufacturers

    • Optimized legacy scripts and resolved database performance issues for an automotive manufacturer
    • Created a CAD wire-harness software mock-up in Java and authored requirement specifications
    • Prepared research documentation on European air-conditioner ISO standards for an electronics manufacturer
    JavaLegacy SystemsCAD

  8. May 2016 - Oct 2016

    Associate Research & Design Engineer · Engineering Services Firm (Philippines)

    Software for a construction-machinery manufacturer

    • Fixed bugs and developed code specifications with unit tests for new features based on Japanese detailed design documents
    JavaUnit Testing

  9. Nov 2013 - Dec 2015

    Full Stack Engineer · Banking Software Provider (Philippines)

    Teller-platform solution for banks

    • Rebuilt a Flex teller-platform application in HTML5 and jQuery
    • Developed reports and web services with Java and SQL; supported the project through go-live
    JavaHTML5jQuerySQLJasper Reports

  10. Apr 2011 - Nov 2013

    Associate Software Engineer · Consumer Finance Company (Philippines)

    Hire-purchase loan system

    • Developed, documented, and tested RESTful APIs across all phases of the SDLC
    • Converted a legacy C-framework project to Spring MVC; migrated databases from Postgres to Oracle
    JavaSpring MVCRESTPostgreSQLOracle

Certifications

  • Professional Scrum Master I2023
  • AWS Certified Developer - Associate2022
  • AWS Certified Cloud Practitioner2022
  • JLPT N3, Japanese Language Proficiency2018

Education

B.S. Computer Science, Network and Data Communications

Bataan Peninsula State University · 2011

Languages

  • English
  • Filipino
  • Japanese (JLPT N3)

Want the full picture?

The case studies show how I actually work through problems.

Case Studies