It is important to note that the Keiretsu are split vertically, no two companies within a keiretsu should be direct competitors. At least such was the case. A

It is important to note that the Keiretsu are split vertically, no two companies within a keiretsu should be direct competitors. At least such was the case. A major counter example is Mitsui and Sumitomo. The Mitsui and Sumitomo banks merged, which triggered partial merges of other Keiretsu companies: except the real estate. Mitsui Real Estate and Sumitomo Real Estate still operate as competitors. Both developing new housing complexes and office towers.