Applications: candidates must already be in Japan. Visa sponsorship: available. Japanese: Conversational. English: Fluent. Japan Dev tags: Engineering, API, Backend, Python, Typescript, AWS, Docker, Github, Slack, Discord.
MISSION
Architect, build, and operate the backend infrastructure powering Shizuku’s conversational AI, live streaming, and social media integrations. Design and implement the orchestration layer that seamlessly unifies LLM, TTS, ASR, and other AI capabilities into a cohesive product experience. Deliver sub-300ms response times at 500+ concurrent YouTube viewers, enabling real-time interactive experiences that feel truly alive.
ABOUT SHIZUKU
Shizuku is a Japan-born AI companion actively engaging audiences on YouTube and X (formerly Twitter). Already running live streams and cultivating a growing community, Shizuku is now entering its next phase of rapid scale.
As the first Japanese startup to receive investment from a16z, we closed our seed round and are on a mission to bring Japanese entertainment × AI to the global stage.
TEAM STRUCTURE
Our founding team is led by Aki — co-founding engineer and ML researcher (ex-Meta, ex-Luma AI) — alongside our Engineering Director. As our first backend engineer, you will have a direct hand in technology selection, architectural decisions, and product direction. You’ll work shoulder-to-shoulder with the founding team, contributing to product-level decisions from day one.
KEY RESPONSIBILITIES
- Design, build, and operate the backend services and APIs powering Shizuku’s conversational AI, live streaming, and social media integrations
- Build real-time integration infrastructure for YouTube, X, Discord, and other external platforms
- Architect and implement the orchestration layer integrating LLM, TTS, ASR, and other AI services into the product
- Design low-latency architectures capable of sustaining 500+ concurrent connections with sub-300ms response times
- Design, build, and operate production environments primarily on AWS
- Establish and continuously improve async job infrastructure, state management, monitoring/alerting, testing strategies, and CI/CD pipelines
REQUIREMENTS
- 3+ years of backend development experience across multiple languages, including Python or TypeScript
- Proven experience designing and operating systems involving Web APIs, async processing, and data stores
- Hands-on experience architecting systems with strict real-time and low-latency requirements
- Demonstrated ability to translate ambiguous requirements into clear specifications and drive projects end-to-end — from design through implementation to release
- Ability to work on-site at our Tokyo office (primarily in-office with flexible remote arrangements)
NICE TO HAVE
- Experience building and managing infrastructure on AWS, including leveraging managed services
- Experience developing AI/LLM-powered products or integrating AI APIs
- Experience with LLM post-training, evaluation, or building training pipelines using tools such as ms-swift or Megatron-LM
- Experience building training data curation and evaluation infrastructure
- Hands-on experience integrating external APIs (YouTube, X, Discord, etc.)
- Experience improving operational quality through log architecture, monitoring, and SLI/SLO practices
- Experience operating consumer-facing (toC) products at scale
- Track record of 0→1 product development in startups or small teams
- Ability to read and write technical documentation in English (currently Japanese-first internally; transitioning to a global environment in the mid-term)
WHO YOU ARE
- Learning Agility — You dive headfirst into unfamiliar territory, rapidly acquire the knowledge you need, and convert it into tangible results
- Purpose-Driven Ownership — You reverse-engineer from user value and business outcomes, identify the right problems to solve, and relentlessly drive them to completion
- Comfort with Ambiguity — You thrive without a PM, making product-level decisions through direct dialogue with the founding team
- Humility & Respect — You honor diverse perspectives and communicate with integrity and constructiveness
- Resilience — You stay tenacious and optimistic through adversity, turning obstacles into forward momentum