Mythra

Mythra is one of the deuteragonists of the 2017 video game Xenoblade Chronicles 2. She is one of Rex's girlfriends (along with Pyra and Pneuma) and Pyra's best friend and alternate form (but also her sister-figure). She is also the opposite of Pyra, as Mythra is very sadistic and rude, a horrible cook, and a more aggressive fighter than Pyra. Despite this, however, Pyra always describes Mythra as a "sweetheart" and even regards her as a best friend.

She is voiced by Skye Bennett in Super Smash Bros. Ultimate.

Super Smash Bros. Ultimate
Mythra was one of the characters from ARMS and Xenoblade Chronicles 2 who were considered for the initial release of the game. However, due to development being completed before the announcement of both games in January 2017, Sakurai chose not to include characters from either of those games. However, Mythra was revealed as a newcomer DLC fighter alongside Pyra on February 17, 2021. The two girls were officially released in-game on March 4, 2021 (March 5 in some countries).

According to Masahiro Sakurai, Rex was planned to serve as a sidekick to Pyra and Mythra during battle (a similar case applies to the Ice Climbers and Banjo and Kazooie), and the player would control two characters at one time. However, due to technical difficulties with the idea's implementation, Sakurai excluded Rex, and decided that the player would take control of a solo fighter and Pyra and Mythra would swap during battle instead.