TSE Prime Idiosyncratic Down-Shock Rebound, TOPIX-ETF Hedged: buy a Japanese large cap at the next Tokyo open after its close-to-close return lags the equal-weight JPEQ panel by <=-2.5 sigma, short yen-matched 1306.JPEQ (TOPIX ETF), fixed 5-session clock (JPEQ 1-DAY, ~100 names, market-neutral)

Original Research Lead hypothesis (not seeded). It applies lesson 266's reference-relative down-shock template (promoted on Bybit vs BTC, Hyperliquid vs BTC and ASX gold miners vs a peer basket) to a new venue and asset class: Tokyo Prime large caps on JPEQ. JPEQ has 6 experiments in the 5,007-experiment corpus, and no stock-level shock-rebound test has been run there. The idea also fills the under-represented long-short / hedged bucket (25% vs a 45%+ target). MECHANISM: Japanese large caps have a well-documented short-horizon reversal, which is stronger than in the US and is usually attributed to retail-dominated, liquidity-demanding selling (margin-call 追証 liquidation by 制度信用 longs, NISA retail stop-outs) that market makers absorb at a discount. The trigger measures the shock RELATIVE to the stock's own market, not as a raw return, so market-wide down days do not fire it. The hedge removes TOPIX beta, so the trade earns only the idiosyncratic rebound. SIGNAL: for each panel name i on each session t, residual r_i,t = log(C_i,t/C_i,t-1) - mean_j log(C_j,t/C_j,t-1), where the mean is the equal-weight average over all panel names with a bar that session. z_i,t = r_i,t / std(r_i, t-60..t-1), computed point in time with the std from the 60 PRIOR sessions only. EXECUTION: decide on the session-t daily close and fill at the session t+1 OPEN (the platform's native next_open_fill on session venues, supported). Exit with a market order decided at the close of the 4th session after entry, filling at the open of the 5th session after entry, for 5 sessions of exposure. HEDGE: whenever the long book changes, the strategy re-targets a single netted SHORT in 1306.JPEQ (NEXT FUNDS TOPIX ETF) to minus the total yen notional of open longs, rounded to the nearest 100-unit board lot. JPEQ supports shorts at 1x with 1.10%/yr borrow modelled. PRE-STUDY (Research Lead, frozen rule, daily JPEQ bars 2018-01-04 to 2026-10-30, 100 names): the <=-2.5 sigma trigger fired 2,733 times on 1,115 distinct sessions. The mean next-open to +5-session-open return was +1.11% raw and +0.24% relative to the equal-weight panel. The date-clustered t on the panel-relative return was 1.77. The panel-relative return was positive in 2018, 2019, 2020, 2022, 2023, 2024 and 2025, and negative in 2021 (-0.59%) and 2026 YTD (-0.29%). The +1.11% raw figure is mostly the panel's own drift: the panel is today's top-100 market caps, so it carries survivorship. The TOPIX hedge exists so that the analyst can judge the idiosyncratic leg, not that drift. COST ARITHMETIC: JPEQ charges zero commission and a 3 bp half-spread modelled per fill, so about 0.06% RT per leg and about 0.12% for the hedged pair per unit of long notional (5-day borrow on the hedge is about 0.02%). Expected capture is about +0.24% panel-relative gross, roughly 2x the hedged cost. Against TOPIX it should be somewhat higher, because the survivor panel's residual drift over TOPIX lands in the long arm. CAPS: 8% of equity per long name, at most 6 concurrent longs, at most 3 new entries per session (taking the most negative z first). Maximum same-date gross long exposure is 24% and maximum total long exposure 48%, matched by an equal yen short in 1306 (gross at most 0.96x, net about 0). Names whose single 100-share lot exceeds the 8% budget are skipped (e.g. high-priced 9983), not over-sized. Risk control route (b): a fixed time exit with capped sizing, every position at most 8% of equity, unlevered gross below 1x. No stop is invented; the source template has none.