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Job Description: About Organization Rakuten Mobile, Inc. is an entity established for the launch of its mobile carrier business as an MNO (Mobile Network Operator.) We aim to provide the most competitive and convenient service to meet our customer needs and demands via the innovative use of technology. Defining future world-standard innovations in the MNO industry, we continually challenge ourselves and capabilities. We are looking for talented individuals who are interested in working with us to create and deliver world class solutions. We are looking for a seasoned Senior Penetration Tester with 10–12+ years of hands-on experience in offensive security. This role covers advanced penetration testing, red teaming, and AI security testing. Based in Tokyo, you will work closely with global and Japan-based engineering, product, and security teams. Job Duties Roles & Responsibilities: Penetration Testing & Red Teaming (Traditional + AI): Lead complex penetration tests across web, mobile, API, internal infrastructure, and cloud environments. Execute red team engagements simulating sophisticated threat actors. Perform high-level AI/ML security assessments, including testing LLM-integrated systems. Identify and exploit vulnerabilities and develop proof-of-concepts. Review system and application architectures to identify security gaps. Produce technical reports and present findings to engineering and leadership teams. Contribute to improving internal offensive security methodologies, including those related to AI-enabled platforms. Minimum Qualifications 10–12+ years of hands-on penetration testing, red teaming, or offensive security experience. Strong expertise in web, mobile, API, network, and infrastructure security. Solid experience with cloud environments (AWS, Azure, GCP). Understanding of OWASP, PTES, MITRE ATT&CK, and modern adversarial techniques. Proficiency with tools such as Burp Suite Pro, Nmap, Metasploit, Cobalt Strike, BloodHound, Kali Linux. Strong scripting skills (Python, Bash, PowerShell). Familiarity with AI/ML concepts and LLM-based applications. Soft Skills - Excellent analytical and problem-solving skills. - Strong written and verbal communication abilities. - Ability to work independently and lead offensive security initiatives. - High integrity and responsibility in security testing. Preferred Qualifications OSCP, OSWE, OSEP, OSCE3 GIAC GPEN, GWAPT, GXPN CREST CRT / CCT Cloud security certifications (AWS / Azure / GCP) Experience or research in AI/ML security is a plus Japanese Language : Ideal to have (Business or Technical proficiency preferred) Languages: English (Overall - 3 - Advanced) Looking for members to join our mobile phone business “They cannot succeed if they step into the field at this late date” Some people say Rakuten is reckless in trying to enter the mobile communications business. However, innovation is realized if we succeed when something seems impossible. At Rakuten, we think the world changes when we achieve such changes. Because our history has always been a series of innovations since our establishment. Launching a communication carrier is an opportunity that we have once in our lives. Crack open the current communication industry. Blow new wind into life. Why not create innovation with us? Why not do something big?