Surprise Santa Encounter

The Japanese adore the secular parts of Christmas. They're also rather fond of Santa Claus.

While they won't let it get in the way of the plot too much, they will give a nod to it in some Anime episode plots.

The Surprise Santa Encounter goes like this. The characters are running around doing whatever...and then suddenly, Santa Claus! Right there!

...no, actually, it was someone else wearing a Santa disguise for no particular reason. (Often a main character) We now return to the plot.

Examples of Surprise Santa Encounter include:

Tuxedo Kamen did this in the Sailor Moon S movie, after which he spouts a speech that's nonsensical even for him.
Washuu in Magical Girl Pretty Sammy.
One of the Gennai clones in Digimon Adventure 02 shows up on a sunny beach in Australia. He was dressed as Santa.
- The arc did take place around Christmas, though. Keep in mind that it's summer in Australia when it's winter in the northern hemisphere.
The characters of Pokémon actually did meet Santa in one episode and helped save Christmas from Team Rocket.
- Of course, he used the reindeer Pokémon (at least in one special; in another one made before this Pokémon had introduced any deer Pokémon, he had a pair of flaming unicorn Pokémon).
Ai Yori Aoshi: Kaoru spent Christmas with a real Santa (who, aside from being one of apparently several Santas, inexplicably looks like Aoi) in the prequel first episode of its second season, Ai Yori Aoshi: Enishi.
Video game example: In case 4 of Phoenix Wright: Ace Attorney, Phoenix and Maya run into a man in a Santa costume at Gourd Lake Park, who turns out to be Wright's friend Larry Butz (introduced in case 1).
The initial antagonist of Advance Wars dressed up like Santa in the Japanese version of the game, but they never made a joke about it. In the English version, however, he dresses like a general should...but everyone calls him Santa Claus.
And then there's the overload of Itsudatte My Santa, where a character named Santa, born on the 24th and hating Christmas, meets Santa Mai, a Santa-in-training. Of course, in this version, the magic of Christmas apparently includes a Magical Girl transformation to a blonde with a rack and a caboose not found on any train set...
In School Rumble, Harima, dressed as a Santa for a part-time job, appears out of nowhere to help some of the cast when they get stuck in the floor (and goes unrecognized).
An imaginary Santa appears from time to time to Hayate the Combat Butler, representing his morals and work ethic. When Hayate decides to stop being such a nice guy, though...
- Of course, Santa's an absolute jackass to Hayate, and it says something about your lot in life when even your conscience mocks you...
The Ichigo Mashimaro girls dress up as Santa and his reindeer (with Miu as Santa, naturally), to deliver a copy of Harry Potter to Matsuri...who still believes in Santa.
In the OAV of Kashimashi: Girl Meets Girl, Yasuna dresses up as Santa, complete with flying reindeer magic supplied by Jan-puu, to give Hazumu and Tomari a Christmas-themed "wedding."
Video game example: In Seiken Densetsu 2 (Secret of Mana in the US), the Frost Gigas, a major boss in the game, is revealed after you defeat him to be Santa Claus, who turned into a monster because little children stopped believing in him. Seriously...well, that and he was being affected by tainted magic.
In Kaitou Saint Tail, the Santa is Saint Tail in disguise.
- ...or a pet lizard (ep 12).
In the Hideo Kojima video game Snatcher, the main character runs into a police informant disguised as Santa.
A brief cartoon at the end of first volume of Death Note has a costumed Light ask Ryuk what he wants for Christmas. Apparently, a 39,800 yen television for one of his plans is worth the price, but an Advance SP for Ryuk is too expensive.

Light: Since when do shinigami celebrate the birth of Christ?
Ryuk: Winter in the human world sure is cold...
Light: You bet it is...

- This naturally led to fan edits where Light kills Santa with the Death Note.
  - Or parodies where he takes over the role of Santa, with Ryuk saying "I wanna be a reindeer."
In Shenmue, once it gets around Christmas somebody in a Santa outfit starts wandering the streets. If this troper remembers correctly, they're usually drunk off their ass at night...
In Go Go Sentai Boukenger, Akashi/Bouken Red randomly runs into Santa Claus...who happens to be a ditzy teenage girl in a miniskirt who provides the monster of the week, the Golem.
- Subverted in the recent series, Kaizoku Sentai Gokaiger; the Gokaigers meet a seemingly ordinary street Santa while doing their shopping, right before the episode's plot kicks off. While this Santa isn't actually the real deal, he does provide a special present to the Gokaigers at the end of the episode: the Battle Fever J Ultimate Power (since "Santa" is actually Battle Kenya).
During one episode of Azumanga Daioh, the girls discuss whether or not Chiyo (a ten-year-old) still believes in Santa. Her answer is that she already knows "Santa" is her dad. Cut to Sakaki's imagination, as Chiyo-Dad (a giant, flat orange cat) pops up in a Santa hat: "Merry Chrismasu!"
Finland dresses up as Santa in Axis Powers Hetalia for the Christmas Episode.
Not quite an encounter, but in the game .hack//Quarantine there is a field on the Omega Server where you can see Santa flying through the air in his sleigh.
In the opening sequence of Baccano! Miria Harvent is robbing a candy store disguised as Santa.
Gintama has five characters become all dress up as Santa and visit the same house at the same time. Hilarity Ensues.
Occasionally, you can see Santa flying in the background in Mortal Kombat 9. If you get a double flawless victory then, you get a secret battle. no, not with Santa Claus, with Classic Reptile.
You're Under Arrest has an episode where a burglar goes around dressed as Santa.
Unbuilt Western version: In Tex Avery's Who Killed Who the detective sees a door marked "Do Not Open Until Xmas". Scoffing, he opens it, and runs smack into a very irritated Santa.

Santa: Listen doc, can't you read? (bops detective on head)