Mercari's Shops & Ads Mobile Enabling team shares their 'One Person One Release' experiment, where a single engineer owns a feature end-to-end across iOS and Android. The bottleneck wasn't coding speed but coordination overhead — aligning specs, API contracts, and platform conventions across multiple engineers. By having one engineer own the full delivery, supported by pair programming and AI agents (for PR translation and boilerplate generation), the team shipped faster with fewer inconsistencies. For complex features, they evolved from translating PRs between platforms to generating both iOS and Android implementations from a shared prompt and spec. Key lessons: inconsistent architecture surfaces immediately under this model, systems thinking improves, and AI tools work best with strong structural guardrails.
