Pona

Pona is the het ship between Popo and Nana from the Ice Climber and Super Smash Bros. fandoms.

Ice Climber
In the original game, Popo and Nana were said to be two people living in a village at the foot of a mountain. Suddenly, a Condor comes by and sweeps all of their village’s vegetables away to its nest at the top of the mountain. So Popo and Nana try to climb the mountain and get their vegetables back. Popo and Nana are controlled by Player 1 and Player 2 respectively and are assumed to work together in order to climb that mountain. In Vs. Ice Climber, the arcade version, they see climbing the mountain as a competition.

Super Smash Bros. Melee
The Super Smash Bros. series shows the two of them being the first characters to fight as a tag team. Popo is the controllable "leader" by default with Nana as a CPU ally. However, this is reversed with some of their alternate costumes. The difference between the two is purely aesthetic.

In the game's opening movie, Nana grabs Popo's hand when he's about to fall. The camera then focuses on their smiles, Popo having his mouth open, while Nana has hers closed. They appear again in several gameplay portions and an FMV portion where they give each other a high-five while Ness turns to look at them. When their hands connect, a heart appears between them.

Their Classic Mode trophy claims that they have climbed “many an ice summit in their mountaineering careers”, and that they “chased” vegetables that “inexplicably” fell from the Condor’s Mountain. It also points out that they’re rarely seen apart. Their Adventure Mode trophy points out that a solo Ice Climber won’t be able to make teamwork moves, admitting that it makes the fight harder. It also points out that the “Squall Hammer” is at its strongest when Nana and Popo combine their strength. Their All-Star Mode trophy points out that the “Belay” is best to cover great distances, but won’t allow them to control their landing. It also says that the “Blizzard” is best use in close quarters and that Nana and Popo will freeze their opponents sometimes.

Super Smash Bros. Brawl
Their trophy states that they use their “incredible jumping powers and hammers” to climb to the summit by breaking blocks. They also “grab veggies” and when they catch the Condor at the end, they supposedly “conquer the mountain”. The game also gives them a “Final Smash”, the Iceberg, by which they summon the Iceberg from their original game to freeze their opponents and send them sliding.

The Subspace Emissary
Their role in the story mode is comparatively minor to other characters. They’re first seen climbing a mountain for vague reasons. Seeing Meta Knight going past them, they thought he was bragging about getting to the summit first and get more motivation to reach the top. Hi-fiving after their “victory”, the Ice Climbers witness a confrontation between Meta Knight and Lucario, but keep themselves out of it. Though they are fairly relieved to find out that the loser will be revived by the winner, their relief doesn’t last as they fail to board the Halberd with the two of them and are thrown back to the ground towards another group of fighters. Teaming up with other heroes to fight the Subspace Army and enter Subspace itself, the Ice Climbers are quickly defeated by Tabuu and turned into trophies. Alongside everyone else, they are rescued by Luigi, King Dedede and Ness and join everyone in a final fight against Tabuu.

Super Smash Bros. for Wii U and 3DS
These is the only game in the series since Melee to not have the two of them playable due to technical limitations of the 3DS; however, they do appear as a Trophy, which states that they defeat animals/critters and mentions the Condor as a challenge for bonus points. In addition, their audience cheer from Brawl is in the game's files, and will occasionally trigger, most likely meaning they were close to being in.

Super Smash Bros. Ultimate
Popo and Nana make their playable return, with their Classic Mode being themed after duos, referencing the bond they share.

Fanon
Pona is a rarepair in the Super Smash Bros. fandom. Though the characters originated in the NES game Ice Climber, most people were introduced to that game and them through the SSB series. The characters are generally considered to be defined by whatever information about them the players could read from their appearances in Super Smash Bros., plus the plot described in the manual of their original game.

Nintendo has never given an official explanation to what exactly their relationship is, they could be anything between siblings, cousins, really good friends, platonic partners, rivals or lovers. Those who interpret them as lovers ship the pairing, those who see them as related ship them with other characters. Nana was especially popular in Brawl, because she's the closest thing Smash had to a playable little girl, thus people really enjoyed shipping her with Ness and a few other young boys in the cast.

Since the fourth game will occasionally use their audience chant for the Villager from Animal Crossing, there are some people who theorize that the Ice Climbers (or at least one of them) might be related to them.

Fandom
FAN FICTION

Trivia

 * In Animal Crossing, there is a pink villager named Nana whose catchphrase is "Popo", this may be a reference to the Ice Climbers.
 * The German translation of every Super Smash Bros. game since Melee renamed Popo to "Pepe", since "Popo" is slang for "butt" in that language.