Xayah's and Rakan's loading screens always align themselves to the rightmost side before a game starts and when picked on the same team (to mirror their shared splash art).
Xayah's and Rakan's dual recall animation is divided into three sections, an intro, a middle section, and then an outro. The whole sequence would take 8 seconds if Xayah and Rakan recalled at the exact same time, while the intro and the outro are both (<2 seconds). The system will always play the intro, then it will always play the outro when there is 2 seconds left in the animation, regardless of how long the middle section has played for. This means that the characters will blend from whatever position they are in, to the first pose of the outro part of the sequence. 
Xayah's cloak is actually her wings disguised by Vastayan magic (to blend in with humans).
Gameplay motivations for Xayah include having a source of power originating not from a bow or gun, creating a unique auto attacking experience, and giving marksman players an option to survive difficult situations.
Another ability shared with Rakan that would create a storm cloud that followed them around and could summon a lightning bolt in the area to stun people. The other had a gust of wind that would knock enemies back.
Deadly Plumage was created extremely late in development, only three weeks prior to shipping.
Some possible thematics for Xayah and Rakan included being vampires or being a storm shaman and storm elemental.
Xayah and Rakan share unique interactions depending on the situation.
Both are the first champions to feature ping-related lines.
"I wanna travel the world with you" and "I want your happiness to evaporate" reference April Ludgate from Parks and Recreation ("I wanna travel the world with her", "I wanted his happiness to evaporate").
Xayah is a Lhotlan Vastayan in her early-mid twenties who travels Ionia on a crusade to ensure her people's survival and independence. After meeting and getting in a relationship with Rakan, both travel Ionia to preserve Ionia's natural magic from being controlled by humans.
Xayah and Rakan fought Zed and his Order of the Shadow to prevent them from harvesting a magical grove (sabotaging the Kashuri Armories, the creators of Jhin'sWhisper and other firearms by using Ionia's abundant magic reserves, might be next).