In the Kachidoki area facing Tokyo Bay, home to the city’s hottest market given its proximity to venues for the 2020 Olympic Games, real-estate broker Hayato Jo has a wall full of notices of apartments for sale, with a 20 percent increase in the number of people looking to sell in the area in the past year. Prices in the neighborhood, which surged 25 percent since Tokyo won the Games in 2013, have started to fall from their peak.