Analyze the relationship between 'Nomura Securities' and 'Nomura Holdings' within the context of the input sentence.
Options: platform, owned by, parent organization, headquarters location

He previously held senior roles at Nomura Securities Co, the brokerage unit of Nomura Holdings Inc. After he left Nomura, Saito served as CEO of the Industrial Revitalization Corporation of Japan, a now-defunct state-backed turnaround fund that invested in troubled companies.
parent organization