Pyra and Mythra are 2 sides of the same coin, both sharing a body but are 2 characters opposite to each other. Both being a  'Blade' in the world of Xenoblade 2 they have an American accent. Mythra's character doesn't show until later in the story However Pyra is here from the start.

As this is an abridged Their characters differ from their original versions, Pyra in our abridged is mostly soft spoken but constantly being frustrated by the lack of intelligence of our main protag and in the first is largely confused from a 500 year power nap. 

We haven't gotten to Mythra yet in our script but in the original game she is sarcastic and comes off as spiteful despite meaning well until she grow throughout the plot

They Both share a voice Pyra is more softer and Calm whereas Mythra's is just a tad bit deeper and more smug sounding