A stock index showcasing Japan's best companies is about to include one of its most controversial: the utility behind the worst nuclear disaster since Chernobyl.

The JPX-Nikkei Index 400 picks firms with the best operating income, return on equity and market value to shame executives of those it excludes into boosting profit and shareholder returns.

Tokyo Electric Power Co. will be added when the gauge changes its constituents next month, according to Nomura Holdings Inc., Daiwa Securities Group Inc. and Mizuho Financial Group Inc. Surges in earnings and share price sent the operator of the crippled Fukushima No. 1 power plant into contention for a place.