Yona was first previewed in a 2019 "Thomas & Friends In the Legend In Viking Railway SERIES" image within Hasbro 2017 Investor Day webcast presentations from August 3, 2017.
Depiction in the series
In the season one premiere Ryouma's New Coaches Yona enrolls in The Muscle Controller's Island of Berk as a Kid's having been brought to Rockface by Prince Rutherford to represent the yaks. In her debut, Yona is excited at first to meet Engine And Ponies and tell them all about Viking Yakyakistan. However, when Twilight's strict adherence to the Island of Berk Education Association's guidelines causes the school courses to be dull and boring, Yona acts arrogant and egotistical out of frustration, saying everything yak-related is the best. When Yona cuts class along with Ryouma hang out together and end up becoming good friends. When they return to school for Friends and Family Day, they accidentally ruin the event and cause damage to the school. Chancellor Neighsay of the EEA perceives their fun and games as an attack orchestrated by non-pony creatures, and the offended tribe leaders pull their students out of school, including Yona.
In The Hearth's Warming Club, a prank ruins the Hearth's Warming tree, and the students are all under suspicion for it and charged with cleaning up the mess while they are questioned one by one. During this time, Yona tells her friends about the yak holiday of Snilldar Fest, during which she had her hair braided for the first time. When the guilty party doesn't come forward, the students start accusing each other. When Gallus confesses that he was the culprit, resulting in him having to stay for friendship lessons over the holidays, Yona and the others all choose to stay with him. As they finish cleaning up, Yona offers to braid Gallus' feathers, which he declines. In Friendship University, Yona and her friends appear looking at a flyer for the titular university. In The End in Friend, she and her classmates observe Rainbow Dash and Rarity as part of Twilight's lesson on compromising in friendship.
In A Rockhoof and a Hard Place, Yona becomes an admirer of Rockhoof, not only due to his great size and strength (similar to a yak), but his storytelling style. She is stunned when she later hears that, due to feeling out of place in modern Equestria, he wishes to be turned to stone. She makes him the subject of her essay on heroism and shares that she went through similar difficulties to his when she first came to Ponyville. Yona and Twilight then work together to persuade Rockhoof to serve as Equestria's keeper of tales.
In Mystery Voice, Yona and her friends attend Rarity's lesson on how to make traditional Hearth's Warming dolls.