The Japanese equity market, up 30% this year, exhibits a reversal relationship: short interest rises with the index and declines during pullbacks.

Among Japan's largest equities, both prices and short interest are higher in most cases, consistent with the index-level pattern.

Kioxia Holdings (285A JP) is an outlier in magnitude while showing the same pattern: up 446% YTD on AI infrastructure demand, with short interest as a percentage of float nearly doubling.

As in Taiwan and Hong Kong, short interest and the index level move together: short interest builds during rallies and declines during pullbacks, indicating shorting into strength and covering into weakness.

The pattern is also consistent with range trading or hedging.

The iShares MSCI Japan ETF (EWJ) does not follow the same pattern: its short interest spiked briefly as the market bottomed in April.

The scatter below plots the 30 largest Japanese stocks by market capitalization. All but four are up on the year, and short interest is higher in all but five.

Across the rest of the cohort there is no clear link between the size of a stock’s return and the size of the change in its short interest, though almost every name is higher on both measures, as at the index level. The upward slope of the fitted line comes almost entirely from Kioxia.

Kioxia Holdings (285A JP) makes memory semiconductors and sits in the AI infrastructure supply chain. It is the outlier on both axes, up 446%, with short interest as a percentage of float rising 4.2 points from 5.0% to 9.2%.

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