Kansayaku (監査役): Statutory auditor, a company officer who audits how directors run the company

The statutory auditor is a distinctively Japanese institution. Kansayaku are elected by shareholders, sit alongside the board rather than on it, and have no vote on business decisions. Their job is to audit how the directors perform their duties. They can attend board meetings, demand reports, investigate the company and its subsidiaries, seek a court injunction to stop a director's unlawful act, and represent the company in suits against directors. A kansayaku cannot at the same time be a director or employee of the company or its subsidiaries.

The term is four years. In a public company it cannot be shortened, and removal needs a special resolution of shareholders, which protects the auditor's independence. A company with a kansayaku board needs at least three, with at least half from outside, and in practice at least one serves full time. Non-public companies can extend the term to ten years and can limit the role to auditing the accounts.

Large companies now choose among three structures: a kansayaku board, an audit and supervisory committee of directors (available since 2015), or a nomination committee structure. Many listed companies have moved away from the kansayaku model, but it remains common.

What it means for a foreign employer

Your subsidiary may need one. Check the articles. If a kansayaku is required, the person cannot also be an employee of the subsidiary, though a parent-company employee can serve.
Full-time kansayaku is a senior post. It is often held by a former finance head or senior manager, and is a source of candidates for governance and audit roles.
Do not confuse it with the external auditor. The accounting auditor, usually an audit firm, is a separate statutory role. English titles such as "auditor" blur the two.
Removal is hard by design. Plan appointments around the four-year term rather than expecting to change the person mid-way.

Sources

Companies Act, Articles 309, 335, 336, 343, 381 to 386 and 390.
Companies Act amendment of 2014 (audit and supervisory committee structure, in force May 2015).

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General information for employers, not legal advice. Thresholds and dates are checked against the sources listed and dated above; confirm anything you act on with a Japanese employment lawyer or a licensed labour and social security attorney.