Founding Full-stack Engineer | Osaka or Tokyo / Remote (Flexible) | Multinational Team #225

Company Overview

The company operates a marketing SaaS platform leveraging LINE. As a rapidly growing startup, it utilizes AI technologies to help brands build sustainable and trustworthy relationships with their customers.

In addition to its LINE marketing tools, the company develops and provides a range of services, including LINE 1-to-1 business chat, digital membership card LINE mini apps, and AI-powered call solutions.

■Key Features

• Operates in the C-commerce market, which is estimated to be worth nearly JPY 30 trillion globally and is projected to surpass the e-commerce market in certain countries by 2025
• Achieved 760% business growth over the past three years in the marketing SaaS domain
• Successfully raised a total of JPY 6.3 billion in funding (including JPY 3.5 billion in Series B)
• Ranked No.1 in LINE marketing in Japan
• A global organization with offices overseas and team members representing 20 different nationalities

 

Job Description

Role Overview

You will be responsible for developing an AI-native customer engagement platform that enables enterprises to optimize communication with their customers. Since Day 1, the platform has been adopted by leading financial institutions and is already used daily by thousands to tens of thousands of employees.

As the Founding Full Stack Engineer / Tech Lead, you will lead the creation of a brand-new product area: the Sales Enablement AI Agent. This AI-powered solution is designed to support sales activities before and after customer meetings. You’ll have the opportunity to drive the project from the ground up, taking ownership of the system architecture, technology selection, and overall technical direction.

While authentication will leverage the company’s shared platform, the Sales Enablement AI Agent will be developed as an independent product stream accessible through the global platform menu, giving you significant ownership and technical autonomy.

Since this is a greenfield project, you’ll also have the opportunity to establish a modern AI-assisted development workflow, making full use of LLMs such as Claude throughout the software development lifecycle. As one of the founding members of this new initiative, you’ll play a key role in shaping both the product and the engineering culture.

 

Key Responsibilities

• Lead the architecture design and technology selection for the Sales Enablement AI Agent from the ground up.
• Design and develop AI agent capabilities that support sales activities before and after customer meetings.
• Build the LLM/AI agent foundation, including prompt engineering, Retrieval-Augmented Generation (RAG), and context management.
• Design and implement the frontend experience integrated into the company’s global platform.
• Design authentication and data integration with the company’s shared platform.
• Design and improve infrastructure, performance, reliability, and operational processes.
• Establish AI-first development workflows utilizing LLMs such as Claude.
• Lead and mentor one or two engineers who will join the team in the future.
• Collaborate closely with the Product, Design, AI, and Infrastructure teams

 

What You’ll Gain / Why This Role is Exciting

• The opportunity to build an entirely new product area from the ground up within a rapidly growing business.
• The ability to leverage an existing enterprise platform already used daily by thousands to tens of thousands of employees at major financial institutions.
• Significant autonomy to establish AI-first engineering practices using LLMs such as Claude.
• The opportunity to build products alongside globally distributed Product, Design, AI, and Infrastructure teams.
• Strong ownership, competitive compensation, and flexible working arrangements.

 

What they expect

They are looking for someone who can:

• Someone who embodies a “WOW THE CUSTOMER” mindset and is passionate about building products that directly contribute to customers’ business success.
• An engineer who can balance development speed with the reliability and quality required by enterprise customers, particularly in the financial sector.
• Someone who enjoys making architectural decisions from scratch and taking technical ownership.
• A professional eager to explore AI agent development and redefine modern software development using LLMs.

 

Career Opportunities

• Advance as a Tech Lead or Solution Architect by leading the launch of a new business domain.
• Grow into an Engineering Manager role as the team expands.
• Become a company-wide leader in AI and LLM adoption, helping shape future AI-driven development initiatives.

 

Required Skills & Qualifications

• 5+ years of professional experience as a software engineer.
• Strong full-stack development experience building modern web applications.
• Hands-on experience with frontend development using frameworks such as React and Next.js.
• Backend development experience using Node.js, Python, or similar technologies.
• Experience designing and operating systems with scalability, infrastructure, and performance in mind.
• Proven ability to design system architecture and make technology decisions from the ground up.
• Business-level Japanese proficiency and currently residing in Japan.
• Experience leading, or a strong desire to lead, a small engineering team (1–2 engineers).
• Ability to work proactively and drive projects forward in fast-changing and ambiguous environments.

 

Preferred Skills

• Experience developing applications powered by LLMs or AI agents.
• Knowledge of Retrieval-Augmented Generation (RAG), prompt engineering, and conversational AI design.
• Experience developing products in the financial services domain or sales enablement solutions.
• Experience building scalable SaaS platforms.
• Interest in, or hands-on experience with, AI-assisted development workflows using tools such as Claude.
• English communication skills.

 

Ideal Candidate Profile

• Thrives in ambiguous environments and can move projects forward by forming hypotheses and taking initiative.
• Is passionate about building products and systems from the ground up.
• Enjoys mentoring and supporting the growth of other engineers.
• Takes ownership of technical decisions and can lead projects while bringing others along through collaboration.

 

Compensation & Benefits

Salary: JPY 7,000,000 〜JPY 11,000,000per year
Probation Period: 3 months

Location
The position is based in either Tokyo or Osaka, depending on the candidate’s preference. Fully remote arrangements can be discussed on a case-by-case basis.

The company offers a flexible hybrid work style, combining remote work with office attendance. Frequency of office visits varies, typically ranging from once a week to once a month.

Working Hours

• Standard hours: 9:00 AM – 6:00 PM (includes a 1-hour break; overtime may be required)
• Flexible working hours with core time from 10:00 AM – 4:00 PM
• For employees above a certain grade, a discretionary labor system applies according to company policy

Holidays & Leave

• Saturdays, Sundays, and public holidays
• New Year’s holidays
• Summer vacation
• Bereavement leave
• Paid leave (10 days granted upon joining, with additional days accrued based on length of service)
• Other holidays as specified by company regulations

Benefits & Perks

• Commuting allowance (bicycle commuting permitted)
• Company-provided laptop
• Company-provided mobile phone (for certain roles only)
• Flexible start time program (can be applied for every 2 months)
• Social insurance coverage (health insurance, employee pension, employment insurance, workers’ compensation)
• Life & health support leave
• Coverage of medical check-up expenses
• Childbirth and childcare support programs
• Club activities and social groups

Measures Against Secondhand Smoke: No Smoking Indoors

 

Hiring Process

• Number of interviews: Document Screening →Coding Test→1~4 interviews → Reference Check→Offer
• Application documents required: Resume / CV
• Interview language: Japanese/English

 

Please note: this position is open to candidates currently residing in Japan.