The Japanese apparently get square watermelons by growing them inside of square glass cases. That way they can fit easily into an overcrowded refrigerator, and you can stack things on them.
Square watermelons are expensive though (10,000 yen or about $82). Compare that to regular round watermelons which cost about $15-20 in Japan.
The square boxes they're grown in are the exact dimensions of Japanese refrigerators, which means they fit perfectly.
They have also grown them in heart shapes – which takes 3 years to grow and ones to look like butternuts.
