The marriage of two of the most powerful keiretsu in Japan has moved one step closer this week. Sumitomo Group and Mitsui Group, once arch rivals at home and beyond, have announced they are forming a joint venture pension consulting business next month, providing pension investment advice to both retail and institutional clients. The new entity, Japan Pension Navigator Co Ltd, will have a start-up capital of Y2.5 billion ($23.2 million).