Reshiram is a white-colored, bipedal Pokémon with draconic, avian and mammalian traits. A long, voluminous wispy mane streams out from the upper side of the snout and outwards from its head. The top of this mane is adorned with two protrusions, which resemble ears. Reshiram's face is fringed with spiky features, and it has a small, pointed extension below the chin. Its eyes have blue irises and black pupils. There are two pairs of pointed teeth visible when its mouth is open, one in the upper jaw and one in the lower.
Reshiram has a long and slender neck, with a fluffy, collar-like protrusion jutting out of two gray, glass-like neck-bands. Its arms begin slender and arm-like, but then flare out into a more wing-like appearance, sporting four claws which resemble hands on the leading edge. There are plates at the back of Reshiram's "hands", that sport a similar color to its neck rings. Reshiram has a feathered or furry feature on its chest, with the lower portion protruding outwards to a point. Long feather-like protrusions jut out of its thighs. On its feet are large gray claws, three at the front and one positioned at the back, resembling high heels. Reshiram's tail is a mass of plume and ribbon-like extensions, surrounded by two large bands, similar to the ones around its neck. When its emotions surge, it enters Overdrive mode and its tail lights up with a fiery glow.
Reshiram has a jet engine-like tail, which it uses to accelerate itself when flying at high speeds. It can send flames from its tail into the air to incinerate everything around it. By flaring its tail, Reshiram is capable of moving the world's atmosphere and changing the weather. This tail generator is also activated when influenced by either Fusion Bolt or Bolt Strike, which in turn powers up Reshiram's own Fusion Flare or Blue Flare. In Unova mythology, Reshiram sided with the older brother who sought the truth. As a result, it firmly believes in truth.
Reshiram played a major role in the Best Wishes! Season 2: Episode N arc. It was first seen in N's flashback to his youth in The Name's N!, where saw Reshiram appearing before him, and kept looking at it as it flew away, right after it set fire to his castle. It was later seen in another flashback in Secrets From Out of the Fog!, rebelling against Ghetsis and Team Plasma by burning down N's Castle during a ceremony involving N, Ghetsis and the Seven Sages.
Reshiram appears on the Unova Pokémon League stage. When it appears, it starts a fire on the stage, damaging fighters.
By setting its torch-like tail ablaze, this Pokémon can heat the atmosphere and change the weather. In fact, legend has it that Reshiram's flames are capable of incinerating the world itself, so perhaps the world's continued safety is a sign of its goodwill. Reshiram is said to help those who seek to build a world of truth.
This Pokémon was unavailable prior to Generation V.
Reshiram was first revealed simultaneously alongside Zekrom on both the official English and Japanese Pokémon websites on May 28, 2010. This makes them the first two Pokémon simultaneously revealed worldwide.
Reshiram and its counterpart Zekrom are based on the concept of yin and yang in Taoism, directly referenced by Reshiram's Japanese species: the White Yang Pokémon. According to Ken Sugimori, Reshiram has a light, airy, feminine design to contrast to Zekrom's tough and masculine design. While the white design matches Reshiram's yang species names (yang being characterized by light), its feminine design contrasts with yang (yang being characterized as masculine). In both versions of the 14th movie, however, Reshiram speaks with a distinctly male voice. Reshiram's tail, the center point of its design, is based on an electric turbine. Appearance-wise, it resembles a mix of animals, including a bird, a pterosaur, and a wyvern. The crest on its head and its feathers resemble smoke trails, as well as white fire, which can burn up to temperatures of 1,500 °C (2,730 °F). The mythology about how Zekrom and Reshiram came about, regarding two brothers infighting, also bears some similarities to Romulus and Remus or Cain and Abel. There is also some resemblance to the Zoroastrian belief of two equally powerful deities, one representing light and truth, and the other representing lies and darkness. In this case, Reshiram can resemble Ahura Mazda, due to its light and winged appearance, and the fact that it sided with truth, but also the fact that Reshiram is a Fire-type Pokémon, and Ahura Mazda was associated with fire.
Reshiram is derived from 白 shiro (white). Ken Sugimori has also stated that Re was used because it was a softer sound than Zekrom's Ze, as Reshiram is a less physically powerful character.