• Sole Android developer responsible for the entire app development and maintaining lifecycle, at the healthcare fintech startup “GradeHealthChain.”• Fast iteration, stable and on-time delivery that contributed to its user growth from 80K to 0.3M.• Contributed to users tracking their health checkup results and medical records over time, motivating them to maintain a healthier lifestyle by implementing various features : a reward system and character growth through missions, personalised workout videos, personalised health reports, supplement recommendations, dietary records, and a service to find nearby hospitals/pharmacies.• Developed a Health Grade Calculation SDK and distributed to third party companies.   - Provided partner companies with support in technical issues. - Continually maintained up-to-date SDK manuals. - Applied ProGuard obfuscation to protect the SDK’s source code.• Legacy modernization : Gradually implementing Clean Architecture, Jetpack Compose, Dagger Hilt, Successfully migrated source code from 100% Java to 100% Kotlin.• Accelerated UI development and improved collaboration with designers through the implementation of ‘Log Design System’, creating UI components.