Info posted by the official Xenoblade account on Twitter (https://twitter.com/XenobladeJP) and translated by Nintendo of Europe (https://twitter.com/NintendoEurope)
Noah
>”Noah” (VA: Ryohei Arai) is an 18-year-old soldier of Keves, and wielder of a bright red weapon. He has a slim build, but his physical abilities are quite high. The way he holds his weapon makes him look like a samurai!
>Noah is the “off-seer” of Keves, who mourns for the soldiers who lost their lives on the battlefield. Having experienced the death of many of his comrades on the battlefield, Noah is fighting against a world that only allows him to take the lives of others in order to live.
Mio
>”Mio” (VA: Minami Tsuda) is a soldier of Agnus who freely controls the Twin Ring. She’s one of the fastest, and she’s good at dodging attacks, too! She’s 19 years old, and her ears are kind of distinctive!
>Mio is also the “off-seer” of Agnus. She is sincere, kind, and well-liked by her friends, but she seems to be the type of person who keeps her problems to herself.
Misc.
>In this world where we live to fight and fight to live, we never know when we or our friends will lose our lives. The sound of the flutes of Noah and Mio, two people who have given many lives as departed souls, is both beautiful and somehow sad.
Bonus, a nice pic of them https://i.imgur.com/z8MSgst.png