The scale of the reconstitution, potentially affecting more than 600 names, creates a multi-year overhang for Japanese small-cap equities as the market works out which companies will be phased out from October and which retain enough free-float market cap to survive. Names near the bottom 3% threshold are likely to see reduced liquidity and persistent selling pressure as index-tracking funds pre-position, while 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, but individual small-cap issuers face concentrated pressure well before their formal removal date.---Earlier:Japan weighs more flexibility for GPIF as pension giant reports Q1 gainsTokyo's benchmark index is about to shed hundreds of its smallest, least liquid members, and the small-cap market is already positioning for who gets cut.Summary:Japan's TSE benchmark index is set for its largest reconstitution on record, with analysts estimating more than 600 companies could be phased outA new inclusion rule will remove firms ranking in the bottom 3% by free-float market cap among TSE-listed companies as of AugustRemovals will be phased in gradually from October over a two-year windowSmall-cap issuers are taking defensive steps this month ahead of the change, given that delisting from the index would likely pressure prices and reduce liquidityThe rule change responds to investor complaints that the benchmark contains too many small, illiquid names, which raises index replication costsMizuho said some investors are already shorting small caps expected to be removed, creating scope for short-covering if market cap shifts and companies end up remaining in the indexJapan'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, with the process phased in gradually from October over a two-year window.The scale of the prospective cull 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. The concern for affected firms is straightforward: 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 reconstitution has also created a distinct trading opportunity around the names 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, since 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. With the two-year phase-in window still ahead, the small-cap market is likely to stay volatile as investors continue recalibrating which names will make the final cut. This article was written by Eamonn Sheridan at investinglive.com.