Pillow fights are practically ubiquitous among students getting ready for bed on school trips in Japan.
The students, who used to sleep in yukata on futons spread out across a large room in a ryokan inn, wait for the teacher to let down their guard before erupting almost spontaneously into the fights.
Now these pillow fights have even developed into a competitive sport.
In Ito, Shizuoka Prefecture, a pillow fight competition called Zen Nippon Makura Nage Taikai in Ito Onsen (All-Japan pillow fight championship at Ito Onsen hot spring resort) is now held each February.
The fifth event took place on Feb. 18 and 19. Of the 84 teams from across the nation that applied for the general section, 48 were selected by lot to participate.
In additon to these, nine teams competed in the children's section, and a total of about 450 players took part in this fierce contest.
The Ito city government and the Ito City Tourist Association have organised the event since 2013 in an effort to promote Ito's hot springs resorts and other attractions and revitalise the city.
The rules are based on those developed by students at the Jogasaki branch of Ito High School.
Each side comprises a total of six to eight players - a captain, called taisho in Japanese; a main group of players, including the libero, who specializes in defence; and one to three support players who fetch pillows tossed from the match area.
Matches are held in a gymnasium.
At the sound of a whistle, players tucked into futons and wearing yukata jump up and begin hurling pillows at their opponents like in dodge ball.
If a player is hit by a pillow, they must go to a futon outside the match area. Catching a pillow is prohibited.
One set lasts two minutes. If a captain is hit by a pillow, the set is over.
The first team to win two sets wins the match.
An interesting rule holds that if one side cries out, "The teacher's coming!" the opposing team must sit on their heels or pretend to be sleeping in their futons for 10 seconds. During that time, the caller's team can fetch pillows from the opponent's area to use for their offence.
The pillows are made exclusively for the competition.
They measure 35 centimeters wide by 50 centimeters long, and weigh 800 grams.
"I think one of the event's charms is the visual element of players in yukata fighting on tatami mats, as well as the fun that players get from throwing pillows at each other without worrying about being scolded later," said Naoki Takahashi of the Ito city government's tourism and industry division, the organizer of the event.
"However, a tactical approach is necessary to win. For example, the libero move about on the front lines, and attacks are focused on the opponent's captain."
This year's winner in the general section was a team called Shinshu PELS from Nagano Prefecture.
Graduates of Shinshu University's physical education course, they also won the event in 2014.
Team representative Kaihei Suzuki, 23, said: "I think our teamwork brought us the victory. This sport is much harder than everybody imagines."