Up 30% on No Filing: TMC and Mercury Hit the Limit

Seoul — The KOSPI closed at 7,003.74 (+0.46%) and the KOSDAQ (tech- and small-cap-heavy market) at 893.29 (-0.11%) on Oct 2, 2026, and optical-communications stocks drove the day. TMC (217590) on the KOSPI and Mercury (100590) on the KOSDAQ both rose about 30%, the daily limit in Korea, but neither company has posted a filing on DART (Korea's official disclosure system) in the past seven days. Brils (468670), on its second day of trading, was up as much as 22% in the afternoon and closed 11.99% higher.

At a glance

TMC (217590): up 29.95% with the sector, but the company filed nothing

TMC rose 29.95% to close at 18,440 won, lifted by a wave of buying in optical-communications stocks on hopes for AI data-center spending. Chosun Biz reported that buying appeared to be driven by news of expanded infrastructure investment by U.S. big tech, and Business Post also tied the move to AI data-center expectations. TMC itself has filed nothing, so the rise rests on sector sentiment, not a company announcement.

The stock is up 35.9% in two sessions and 28.9% in five, and 50.7% since Aug 27 (12,240 won). Trading value was 99.5 billion won, roughly 22% of its 444.3 billion won market capitalization. Foreign investors net bought 83,416 shares on Oct 1. A Eugene Investment & Securities report dated May 28 described a supply shortage after a U.S. plant visit, but it is four months old and does not explain today's move. TMC also jumped 20.96% in a single day on Sept 14, so this is not its first spike.

Two things to watch: whether the company confirms U.S. orders or earnings in a filing, and whether trading value holds up on the next session. A theme-driven rally tends to unwind quickly once volume fades.

Mercury (100590): follows New York's optical rally to the limit, again without a filing

Mercury rose 29.8% to close at 6,250 won, tracking a surge in optical-related stocks in New York the previous night. News1 attributed the move to that overnight rally, and Maeil Shinmun cited rising demand expectations from AI data-center investment. Mercury has filed nothing in the past seven days. A headline from job-post.co.kr mentioned a turnaround to profit in its optical unit, but the company has not confirmed that in a filing.

The stock is up 31.9% over two days and 25.1% over five. Trading value was 23.8 billion won, about 22% of its 107.1 billion won market capitalization. Foreign investors net bought 50,996 shares on Oct 1. Mercury also jumped 30% in one day on Sept 9, then drifted in the 4,700 to 5,000 won range, and today's close is well above that band. Daehan Optical rose only 4.71% the same day, so gains varied widely across the group.

Watch whether the optical-unit turnaround shows up in reported quarterly results, and whether the gains get given back within days, as happened after the September spike.

Brils (468670): up 12% on day two, but the afternoon gain was cut roughly in half

Brils (second trading day) rose nearly 12% with no new catalyst, extending the buying from its debut. It closed at 34,100 won, up 11.99%. At 1:30 p.m. it was at 37,300 won, up 22.5%, before the gain shrank. The only company-related notice is the exchange's Oct 1 caution flag for high single-account trading volume. No filing or report explains the rise.

Trading value was 436.1 billion won, more than the 387.5 billion won market capitalization, meaning more than the company's entire value changed hands in one day. On day one, individuals net bought 1,756,768 shares while institutions net sold 1,327,874. Heavy institutional selling at the start is a weight on any continued rise. It is newly listed, so there is no earlier price to compare.

The lock-up expiry dates for institutional shares and the amount of tradable stock matter here, as does whether trading value stays at this level on the next session.

Stocks we covered last time: what happened next

All three rose again. The biggest gain went to LK Samyang, whose first rise had no confirmed reason. A firmer verdict did not mean a bigger move the next day.