Senior Network Security Engineer, System Security Engineering Group - Security Engineering Section (RMI Security Eng. & Ops Dep)

Job Description:

About Organization

The Security Engineering & Operations Division is responsible for the design, operation, and continuous improvement of security across Rakuten Mobile’s network, cloud, and platform environments. The Security Engineering Department strengthens controls for network perimeters, defensive infrastructure, and cloud-native platforms to provide a resilient and trusted telecommunications foundation. Within this department, the System Security Engineering Section drives zero-trust architecture, micro-segmentation, and secure operational automation. We offer the opportunity to lead complex security engineering initiatives—from design and implementation to operational optimization—in one of the world's most advanced telecom environments.

Job Duties

• Kubernetes Security: Design, implement, and improve network and cluster security for Kubernetes-based environments.
• Traffic & Application Security: Design and operate load balancing, WAF, SSL/TLS, and traffic control solutions using F5 technologies (LTM, ASM/AWAF).
• Perimeter & Access Security: Design, configure, and troubleshoot Cisco security products, including ASA, Firepower, ISE, and Umbrella.
• Cloud Security Architecture: Establish security baselines for cloud environments, focusing on IAM, network isolation, logging, monitoring, and vulnerability management.
• Incident & Vulnerability Management: Investigate security incidents and audit findings, driving permanent remediation and preventive measures.
• Operational Excellence: Improve operational automation, define configuration standards, create technical documentation, and provide mentorship to junior engineers.
• Cross-Functional Collaboration: Partner with network, platform, development, SOC, and GRC stakeholders to drive integrated security improvements.

Minimum Qualifications

• 8+ years of hands-on experience as a Network or Security Engineer.
• Proven experience designing and operating network, cluster, and container security for Kubernetes environments.
• Extensive experience building and troubleshooting F5 products (LTM, ASM/AWAF).
• Practical experience with Cisco security products (ASA, Firepower, ISE, Umbrella).
• Working knowledge of cloud-native security, including IAM, networking, and vulnerability management.
• Demonstrated technical leadership in incident response and risk reduction initiatives.
• Professional proficiency in English (technical communication, documentation, and stakeholder coordination).

Preferred Qualifications

• Professional certifications: CISSP, CCNP/CCIE Security, CKS, or Cloud Security (AWS/Azure/GCP).
• Experience automating security operations using Terraform, Ansible, or Python.
• Deep knowledge of Zero Trust, Microsegmentation, SASE/SSE, SIEM, or SOAR.
• Experience in large-scale, high-availability environments (Telecommunications, Finance, or E-commerce).
• Proven track record in team leadership, mentoring, and technical standardization.

Work Environment

• Department: System Security Engineering Section, Security Engineering Department.
• Collaboration: Work with global teams across Japan and overseas.
• Tech Stack: Kubernetes, F5 LTM/ASM/AWAF, Cisco ASA/Firepower/ISE/Umbrella, Cloud Security Services, Linux, CI/CD, and monitoring/logging platforms.
• Location: Japan (Tokyo or Osaka)

Languages: