Senior Software engineer, iOS (AI/LLM) - Mercari
Job Description
- Employment Status: Full-time
- Work Hours: Full Flextime (no core time)
- Office: Roppongi
For more details, see the section on our Careers site.
Organization/Team Mission
Mercari Engineering Principles
Mercari Engineering Principles are a shared understanding that serves as the foundation of engineering beliefs and behavior at Mercari. The Engineering Principles are designed to complement the organizational identity (Mercari’s mission, values, and culture) from an engineering viewpoint.
These principles ultimately help us achieve Mercari’s mission by defining the ideal state we seek to realize in the long term.
- Passion For The Product
- Grow Together
- Solve Through Mechanisms
- Collaborate Openly
For more details, please see the following link:
The AI / LLM Team’s mission is focused on two core pillars, "building" and "enabling" – delivering new AI-driven features and user experiences to maximize product-facing impact for Mercari's business. We do this both through independent initiatives owned by our team, as well as by horizontally collaborating with product and engineering teams across the entire organization
As an iOS engineer, you will work on building features with our machine learning, backend, and infrastructure members as well as collaborating with other feature-owner iOS engineering teams.
See here for more information about our mission and values.
Responsibilities
- Design, implement, and maintain high-quality iOS features using Swift and modern iOS frameworks.
- Own end-to-end feature development, from requirements definition through architecture, implementation, testing, and release.
- Lead architectural design for complex features and system components, ensuring maintainability, scalability, and reliability.
- Optimize app performance, startup time, memory usage, and stability across diverse devices and OS versions.
- Work closely with machine learning, backend, infrastructure, product, and design teams to deliver seamless mobile experiences, as well as other feature-owner iOS engineering teams.
- Contribute to and evolve Mercari's mobile platform, SDKs, and shared modules used across teams.
- Drive high code quality through code reviews, automated testing, CI/CD improvements, and rigorous documentation.
- Champion engineering best practices and contribute to guidelines and standards across Client Engineering.
- Stay current with the latest developments in iOS, Swift, UIKit, SwiftUI, concurrency, and mobile architecture patterns.
- Bring innovative ideas to improve user experience, developer experience, and operational efficiency.
- Take ownership of initiatives that span multiple teams, driving alignment and technical decision-making.
- Mentor junior and mid-level engineers, helping strengthen the overall technical capabilities of the team.
Unique Challenges
- In this position, you will develop iOS features for AI-driven solutions that leverage Mercari Group’s vast data assets, creating high-impact user experiences for tens of millions of users.
- Deliver highly performant and reliable functionality in a fast-paced environment with complex product requirements.
- Bridge consumer-grade UX expectations with robust engineering architecture and infrastructure.
- Influence platform-wide technical strategy, shaping the future direction of Mercari’s mobile ecosystem.
- Lead cross-functional efforts in ambiguous problem spaces where user needs and technical constraints must be balanced.
Qualifications
Required Experience/Skills
- Shared belief in the mission and values of the Mercari Group.
- Bachelor’s degree in Computer Science, Engineering, or equivalent practical experience.
- Strong proficiency in Swift and iOS development frameworks (UIKit, SwiftUI, Combine, Foundation).
- Solid understanding of mobile architecture patterns (MVC, MVVM, Clean Architecture, VIPER, etc.).
- Demonstrated experience with large-scale mobile applications and complex codebases.
- Experience integrating with backend APIs and asynchronous/concurrent programming.
- Strong analytical and problem-solving skills; ability to navigate ambiguity.
- Excellent communication skills and ability to explain technical concepts clearly.
- Passion for building user-facing mobile products.
Preferred Experience/Skills
- Experience with large-scale mobile apps serving millions of users.
- Expertise in performance optimization, instrumentation, and mobile observability (e.g., crash analysis, metrics).
- Experience with SwiftUI, concurrency (async/await), and modern iOS platform capabilities.
- Contributions to open-source iOS projects or active involvement in the mobile community.
- Experience driving technical initiatives across multiple teams or owning platform-level components.
- Familiarity with CI/CD for mobile, automated testing frameworks, and release management.
- UI/UX sensitivity and an eye for detail in crafting polished user experiences.
Language
- English: Independent (CEFR B2) Required
- Japanese: Independent (CEFR B2) Optional
For details about CEFR, see here.
About the Company
Our Mission
Mercari is a Japan-based company with the mission of “creating value in a global marketplace where anyone can buy & sell.” Having continuously worked toward this goal since our founding in 2013, we are now transforming from a startup into a global player. While this transformation brings its own specific set of challenges, we believe that solving them one after another will allow us to fully achieve our mission. Are you interested in working together to take on these exciting challenges?
Our Culture
Mercari’s culture has been central to the company since our founding, with the three core values of Go Bold, All for One, and Be a Pro. In addition, the “Trust & Openness” value was introduced to embody our culture of mutual trust, where information remains transparent and rules are kept to a minimum. Regardless of how big Mercari gets, our culture is essential to achieving our mission and will be promoted throughout our organization.