Mizuho Securities is building its structured credit and debt capital markets business.

Losses from trader error in December should have been reversible, securities house claims.

The Tokyo Stock Exchange found that a malfunction in its new and trouble-prone trading system prevented Mizuho Securities from being able to cancel the mistaken J-Com order.

A three-way merger has created Mizuho, Japan’s and the world’s biggest bank by assets. If the deal works – and legal issues will postpone full integration for some time – the new leviathan may be a powerhouse. But is management up to the task? And will Japan’s notoriously difficult market let them do what they want?