Illya: Shirou, once you get inside, you wouldn't want to get out... It's like a magic spell's been cast on you...
In Japan, most homes lack central heating, and are very thinly insulated, so most people rely on electric space heaters. The most common form is the kotatsu ("heater table") which consists of a low table with an electric heater built into its underside, with a very thick quilted drape around it. People wanting to stay warm seat themselves on the floor under the table. The drape keeps the heat trapped underneath, and it travels through the inside of clothing to heat the sitters' bodies. If they're so inclined, they can scoot almost all the way under the table and use it as a makeshift heated bed, although there is a belief that falling asleep under the kotatsu makes you vulnerable to catching a cold.
Mikan (known as satsumas in the west) are a variety of mandarin orange that are in season during the winter. Oranges are considered to have a lot of nutrients important for getting through the cold season, so it is common to see a bowl of them on the table. For many Japanese, a kotatsu holding a bowl of tangerines is the archetypal symbol of winter.
Kotatsu usually show up in Slice of Life moments, with a (generally female) group of friends sitting around one, murmuring about how warm and comfortable it is, rambling on about their lives, napping, and every single one complaining that someone else should go get some snacks. Often prime Sleep Cute territory. They are also a useful vehicle for Naughty Under the Table hi-jinx.
- In Love Hina, Keitaro, Naru and Mutsumi frequently study at a Kotatsu together.
- In Mahou Sensei Negima! Makie uses her gymnastics ribbons to grab snacks without getting up.
- Azumanga Daioh has Osaka falling asleep under a kotatsu while at Chiyo's house and having a weird Dream Sequence. When they leave, she bids it farewell and reminisces about it on the way home...
- Sgt. Frog:
- In one manga chapter, (Fuyuki and Natsumi. Guess who has to go get the snacks?) Meanwhile, Keroro attempts to convince them to come out from under it so they can take him to the store to buy Gundam models.
- In one episode, Keroro sees Fuyuki sleeping with his head sticking out of a kotatsu and immediately does a double-take, imagining Fuyuki as the GP-03 Dendrobium Orchis◊ from Mobile Suit Gundam 0083: Stardust Memory.
- Lucky Star episode 13 has an extended Seinfeldian Conversation about kotatsus.
- Strawberry Marshmallow, of course, has the Slice of Life version a couple of times. In one episode picture, Miu and Matsuri share the space underneath.
- Minami-ke devotes considerable time to kotatsu antics and also had an episode or two involving oranges in one of those scenes.
- Persona 4 includes kotatsu scenes in the later parts of the game. Nanako wants one, and the party eventually gets one for her. The day they go to get it (after she's been kidnapped, rescued, and hospitalized) is the day Adachi calls you to tell you her condition took a turn for the worse.
- In Persona 4's Updated Re-release, Golden, when the protagonist falls violently ill, Teddie, whom was staying to keep the player company, ends up putting him beneath the kotatsu. Several other party members lampshade the decision when they come over to check on him.
- Cross Game: On New Year's Day, Kou and Aoba both fall asleep under the kotatsu leading to a Sleep Cute situation. Heartwarming since they are normally fighting with each other.
- Hidamari Sketch has the Slice of Life use, natch.
- In Urusei Yatsura, Kotatsu Neko is the ghost of a cat that froze to death, so its spirit is now attracted to heater tables.
- Kotatsu Neko, on the other hand, is a live-action film recently adapted to anime, about two (living) cats that spend most of their time under a kotatsu.
- In Dear, the Big Bad Evil Overlord Subaru... spends his days under the kotatsu sleeping or watching television. (When he isn't attempting lay Komomo on top of it...)
- The Kotatsu table proves to be the bane of Chiaki's existence in Nodame Cantabile. IT TURNS PEOPLE INTO LAZY SLOBS! He has Nodame to thank for introducing it to him, and almost ruining his life there and then. When he finally gets the chance to clean up his apartment and throw the table away, Nodame takes it from the trash and mentions how someone threw out a perfectly good Kotatsu. Chiaki was less than thrilled about it.
- Yui from K-On! is practically addicted to the kotatsu, which isn't helped by her sister's pampering.
- Tamaki from Ouran High School Host Club has an obsession with them particularly when he first came to Japan. Probably because they symbolize the kind of close, warm family life he so desperately wants.
- It apparently runs in the family because when Kyouya meets Tamaki's mother on a class trip to France she excitedly asks him if he owns a kotatsu.
- In Sayonara, Zetsubou-Sensei, there are occasional scenes of Nozomu at home, typically with his nephew, Majiru and students Matoi and Kiri who live there as well, and in such scenes, he's often lying under a kotatsu.
- In Kamichu!, Yurie spends an entire episode sitting, lying, sleeping, and even using the phone under the family kotatsu. Her solutions to avoid leaving it are at times rather creative.
- Colorful spices up the standard ecchi fare in one episode by having the lecherous male get his just desserts while trying to devour the tasty view.
- In Axis Powers Hetalia the members of the Axis gather around a kotatsu to sign the Tripartite Pact. It even pays homage to the page image.
- In the webcomic The Escapades of The Blue Kotatsu owning one justifies the heroine's superhero name.
- In Rinne, Ageha the Shinigami (who has a crush on the titular character) buys one of these for 100,000 yen, duped into thinking it's a "friendly square" that generates an intimate space with anyone. Instead of getting her closer to Rinne the way she wanted though, in the end it brings the main cast closer together.
- The Morning Musume song Mikan is about childhood memories, such as eating oranges around the kotatsu.
- Since Gintama's animation team likes to pull out the New Years footage for gags, we see the kotatsu + tangerines + dirty dvd cover combination fairly often.
- As a young girl, Tsukimi from Princess Jellyfish used to fall asleep curled up under a kotatsu blanket after being fed a good meal by her mother.
- In 3-gatsu no Lion, Rei and the Kawamoto family spend much time under one during his stay in their house around New Year's. He later uses this as similie for the differences between his time with the Kawamotos, which is generally filled with "warm" experiences, and his time alone in his own home, which is cold and depressing.
- Some incarnations of Dian from Jewelpet give him an odd obsession with kotatsus. This is justified in the first series because he was stuck in an ice prison for a long time.
- Seen at the Furukawas' in CLANNAD. One also features when Nagisa and Tomoya's friends visit them for New Years' in ~After Story. Sunohara also has one in his dorm room.
- Rabbit Team from Girls und Panzer apparently has one hidden in their tank, as they are seen huddling under it while besieged by Pravda in the middle of a snowstorm.
- Tohru wins one at a lottery in episode 11 of Miss Kobayashi's Dragon Maid. She, Kanna, and Kobayashi spend a good chuck of the episode huddled under it. Chapter 48 of Kanna's Daily Life has the whole family go shopping for a new one when the old one breaks.
- One chapter of Sleepy Princess in the Demon Castle centers around Princess Syalis making one so she can stay warm in the unheated Demon Castle through the winter.