Senior Data Scientist - Demand Forecasting (JPY 7M - 12M | Remote / Hybrid in Japan)

Senior Data Scientist / Time Series Specialist (PoC & Forecasting)

About the Role

We are looking for a Senior Data Scientist to lead our advanced time series forecasting and accuracy-improvement initiatives. In this role, you will not just build models—you will drive end-to-end problem solving, from data-driven hypothesis formulation and hierarchical forecasting to local PoC verification.

If you thrive on untangling complex data structures, tackling seasonal patterns, and translating ambiguous business requirements into high-impact technical solutions, we’d love to have you on board.

Key Responsibilities & Scope

Primarily support in the following areas:

1. Hypothesis Formulation: Drive accuracy improvements through rigorous, data-driven analysis. (Note: Grounded in data-backed investigation).
2. Evaluation Frameworks: Design structured evaluation frameworks to determine improvement feasibility, delivering clear outputs that support PoC result interpretation and expected accuracy gains. (Includes scoping out the rationale behind PoC results).
3. Error Isolation & Root Cause Analysis: Isolate accuracy-deteriorating segments and perform deep-dive cause analysis to answer "why accuracy is dropping."
4. Impact-Driven Prioritization: Prioritize improvement candidates based on expected business impact and implementation feasibility, selecting optimal items for PoC verification.
5. Local Environment Verification (PoC Level): Conduct robust testing and verification in a local environment. (Note: Production deployment is handled separately by the customer team).

What You Bring (Technical Expertise)

1. Time Series Forecasting Mastery

• Classical & ML Approaches: Deep knowledge of classical methods (ARIMA/SARIMA, ETS, Prophet) and modern ML approaches (XGBoost/LightGBM with lag features).
• Hierarchical Forecasting: Experience with multi-level forecasting (SKU → style → category → region/channel) and reconciliation methods.
• Complex Patterns: Proven ability to handle complex seasonality (weekly/monthly), trends, holidays, and promotional effects.

2. Data Quality & Advanced Testing

• Feature Engineering: Crafting robust features (lags, rolling statistics, price/promo features, calendar/holiday signals, stock-outs, lead times).
• Evaluation & Backtesting: Selecting appropriate metrics (WAPE, MAPE, sMAPE, RMSE) and designing backtesting strategies (rolling/expanding window).
• Model Insights: Strong grasp of bias/variance tradeoffs, regularization, and model interpretability (using tools like SHAP).

3. Tech Stack & Data Wrangling

• Advanced SQL & handling large-scale datasets.
• Python Ecosystem: Expert-level proficiency in pandas, numpy, scikit-learn, statsmodels, prophet, and tree-based models (XGBoost, etc.).
• Cloud & Tools: Experience with cloud environments (GCP), workflow orchestration (Airflow), and data warehousing (BigQuery).

Core Competencies & Engineering Culture

We value autonomy, high ownership, and proactive collaboration:

• Strategic Communication & Ownership: You don’t wait passively for clean requirements. You lead discussions, ask sharp clarifying questions, align stakeholders on priorities, and communicate risks early.
• Deadline & Delivery Reliability: You take ownership of timelines, set realistic scopes, and ensure complete transparency through regular updates and proactive early escalation if risks arise.
• Systematic Problem Solving & Catch-up: Ability to rapidly digest complex, undocumented business systems, interview stakeholders to uncover hidden issues, and turn fragmented information into structured action items.
• Quality Assurance & Craftsmanship: Active code-review participant, independent test-case designer (happy paths, edge cases, boundaries), and an advocate for clean documentation (design docs, runbooks, incident logs).

Why Join Us?

• Work on challenging, high-impact forecasting problems with cutting-edge data stacks.
• High degree of autonomy and direct impact on business accuracy and performance.
• A collaborative culture that values technical rigor, clean code, and intellectual curiosity.