Take context from the input text and decide on the accurate relationship between 'Nomura Securities' and 'Nomura Holdings' from the options provided.
Options: parent organization, headquarters location, owned by, platform

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