Mobile App Engineer (Langaku)

  • Tokyo
  • Partial Remote
  • Full-time
  • November 4, 2025
Conditions
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¥6M ~ ¥9M /yr
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Apply from Japan Only
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No relocation to Japan
(No visa sponsorship from overseas)
Requirements
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Language Requirements
Japanese: Business Level
English: Business Level
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Minimum Experience
Mid-level or above

Primary Responsibilities

  • Designing, developing, operating, testing, and documenting mobile applications using Flutter.
  • Enhancing productivity and quality through automation of testing and operations.
  • Collaborating with product managers and designers to design user experiences and features that solve user problems.
  • Making technical decisions and building/managing development schedules.

 

Technical Stack:

  • Frontend: Flutter
  • Backend: Python
  • Infrastructure: AWS, GCP

 

Basic Qualifications

  • 3+ years of experience in developing with Flutter.
  • Ability to design and develop software with maintainability and performance in mind.
  • Ability to design and propose improvements for mobile apps considering user experience.
  • Experience in team development using Git, GitHub, etc.

 

Preferred Qualifications

  • Experience in developing BtoC mobile applications.
  • Experience in building and operating infrastructure using AWS.
  • Knowledge and understanding of UI/UX design, and experience in designing.
  • Experience in implementing and operating automated testing for frontend apps.
  • Knowledge and experience with server-side development using Django.

 

The Ideal Candidate

  • Someone accustomed to continuous learning
  • Able to approach problems by formulating and then verifying hypotheses
  • Enjoys communicating with people from different fields and backgrounds
  • Able to take ownership and handle working independently
  • Strong interest in Mantra's focus areas (manga, language, machine learning)

 

Selection process

  • Document screening (resume, detailed career and job history, portfolio)
  • ~3 Interviews
  • Final meeting to discuss terms of employment and compensation

Mantra has been developing machine learning technologies specifically for the entertainment industry.

Mantra's machine translation engine consists of computer vision / natural language processing technologies for manga.

Here are two services that use the technologies:

  • MANTRA ENGINE - A translation support platform for businesses
    Mantra provides a multilingual translation engine developed for manga and webtoon, and is widely used by publishers and distribution services. By integrating most steps of the translation workflow, this unique solution enables simultaneous distribution worldwide.

  • LANGAKU - English learning service with Manga
    Langaku helps learners improve their English by reading Manga. Readers can adjust the language difficulty, access text audio for listening practice, and read in multiple languages, making learning easier and more fun. Langaku brings the joy of Manga to English language learners.
View Mantra's company page

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Mobile App Engineer (Langaku) at Mantra
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