Uwabami
Uwabami, or yamakachi, is the name of an unknown species of large constrictor snake said to inhabit Japan. These snakes are reported to inhabit the much more sparsely populated mountainous, forest-covered interior. The largest snake native to Japan outside Okinawa is the Japanese rat snake, though they rarely exceed seven feet in length. Uwabamis are said to average 20 to 30 feet, which is two thirds longer than the longest known snake, the reticulated python.
Uwabamis have been commonly featured in Japanese folklore since the 15th century, though modern accounts only started appearing in the 1970s. For instance, on May 26th, 1973, a group of forestry workers came across a snake splayed out across a trail near Mt. Tsurugi, in the Tokushima prefecture. About 16 feet of the snake was visible, with the rest being obscured in the foliage. They assumed its total length was around 30 feet and "was as wide as a propane tank." The snake was covered in bluish-black scales and had a whitish belly. Strangely, they claimed that before it slithered away, the snake made a chirping/piping call, which may seem quite far-fetched, although many species of snakes can vocalize.
The forestry worker's sighting caused the local people in the area to fear for their safety, and many of them came forward with their sightings. Just a month later, a group of volunteers started searching for uwabamis. Although unsuccessful in finding any, a 40 cm (16 inch) wide track was found. Assuming the track was made by a snake with a width-to-length ratio similar to that of an anaconda, the snake would be more than 34 feet long.
In the Kochi Prefecture, a group of three men taking a hike claimed to have come across a 26-foot long snake on a trail. They initially believed it to be a fallen utility pole, but when they got closer, it slithered away.
On January 24th, 1987, a farmer named Asakura Kayoko, reported seeing a giant snake on his farm in the Kochi prefecture. After hearing his chickens panicking, he went to investigate. He came across what he initially thought was a log that somehow got on top of his chicken coop, but then quickly realized it was a 23-foot snake swallowing one of his chickens. One of his dogs bolted at the snake, but it quickly slithered away.
At an unknown time in the Izu prefecture, a 30-foot long albino snake was spotted by construction workers in the woods behind a hotel. Many of the hotel staff were understandably frightened, and some refused to work there for several days after. An investigation looking for the snake didn't manage to find anything.
Although sightings of uwabamis seem to stop in the early 90s, there are likely more recent reports that have never been translated and are only known in Japan. Some have theorized that "uwabamis" are actually escaped exotic pets, though this is unlikely, as no known snake species regularly exceed 20 feet.