He sold 100 more futures contracts. Two hours later, he sold another 100. His bet against the Nikkei had risen to about $275 million. He would lose $1.4 million for every 100-yen increase in the index.

His logic for hanging on to the trade until the U.S. open, at 10:30 p.m. Tokyo time, was this: Panic would grip American investors returning from a weekend after they saw the scope of Asian selling, including Shanghai’s 8.5 percent plunge. That would trigger selling, which, in a feedback loop, would pull Nikkei 225 futures down violently amid the thin volume of late- night trading.

“I figured there would be a lot of fear around the U.S. open and that’s what I was aiming for,” he said.

On cue, the Dow Jones Industrial Average fell more than 6 percent in early trading. Nikkei futures tumbled again, dipping 1,250 yen below the 3 p.m. closing level. CIS, home in his pajamas, finally cashed out his short position. His profit had hit $27 million.

“Too Delicious”

There was still more money to be made from the panic though. Some investors that night were willing to pay a hefty premium for options that protected against the Nikkei crashing below 10,500. That would be a collapse of almost 40 percent. In CIS’s view, these investors were looking to buy insurance against a near impossibility.

He was happy to take the other side of that trade. The contracts were worth another $250,000 to him. He made the first deal within 10 seconds of what would prove to be the market’s bottom at 10:34 p.m.

“Too delicious,” he tweeted.

About an hour later, as he became more confident in a rebound, he started buying Nikkei futures. Now the play was the opposite of the short bet he’d started the day with. By 1 o’clock Tuesday morning, he’d accumulated 970 contracts, a $145 million wager that the market would start to climb.

He made one more trade before bed: a few more option contracts sold to straggling panickers. Those were worth $6,250. By now, at 1:40 a.m., he was a rich man stooping to pick up pennies.