Japan's Tokyo Stock Exchange benchmark index is heading for its largest reconstitution on record, with analysts estimating that more than 600 companies could be phased out under a newly introduced inclusion rule.

Under the change, firms ranking in the bottom 3% by free-float market capitalisation among TSE-listed companies as of August will be removed from the benchmark. The process will be phased in gradually from October over a two-year window.

The scale of the prospective removal is already prompting small-cap issuers to take defensive steps this month, as companies close to the threshold move to protect their standing before the removals begin. Delisting from the benchmark would likely pressure share prices and reduce trading liquidity, given the loss of passive and index-tracking demand that comes with inclusion. For companies clustered near the bottom 3% cut-off, that pressure is likely to build well ahead of any formal removal date, as the market begins pricing in the eventual outcome.

The rule change is a direct response to longstanding investor complaints that the benchmark has become bloated with small, illiquid names — a composition that has raised the cost of replicating the index for passive funds. By trimming the tail of the index, the TSE aims to improve the overall liquidity profile of benchmark constituents and reduce tracking costs for the large pools of capital that mirror the index. The overhaul fits within Japan's broader market reform push that has gained momentum since the TSE's 2022 market-section restructuring, which consolidated listed firms into Prime, Standard, and Growth segments and was followed by governance campaigns urging companies trading below book value to improve capital efficiency.

Names near the bottom 3% threshold are likely to see reduced liquidity and persistent selling pressure as index-tracking funds pre-position. The reconstitution has also created a distinct trading dynamic around the companies most at risk. Mizuho said some investors are already shorting small caps expected to be removed from the index, positioning for the liquidity and price pressure that typically accompanies benchmark exclusion.

That positioning carries its own risk, however. Market capitalisation rankings can shift over the run-up to the August measurement date, and Hatano noted there is scope for a sharp short-covering rally in any company that ultimately avoids removal after being expected to face it. Short interest in expected removals could unwind sharply if market capitalisation shifts push borderline companies back above the cut-off.

The two-year phase-in window means the effect on the broader index and passive flows should be gradual rather than a single disruptive event. However, individual small-cap issuers face concentrated pressure well before their formal removal date. With the phase-in period still ahead, the small-cap market is likely to remain volatile as investors continue recalibrating which names will make the final cut.

Separately, Japan is weighing more flexibility for GPIF as the pension giant reports Q1 gains.

Source: Investinglive