I've been eyeing this thread for quite a while but was struggling to keep my response concise ;;
Reiner is an amalgamation from two of three my favorite OCs
(original characters) that I've written long time ago. One is a human who later ascended into a celestial, and the other is an
arahitogami. It only make sense to me to create him as a Middie Hyur. But then I came to a hard decision of whose trait I'd like to take and which one's to give up.
In the end I used the former's physical traits and the latter's personality
(largely). His emerald green & hazel green eyes are to represent his distrustful, evasive personality. Narratively speaking, flowerpins/corsages often being present on his glamour plates are to represent his subtle, unspoken sentiment. His youthful-bratty glamour aesthetic are to represent his desire to be free of burden.
To ease into XIV's lore, I wrote that the latter performed some sort of esoteric magical experiment that gone wrong back in his home universe, which lead to his spiriting away into the realm of hydaelyn then morphed to a shade of his bestie
(the former) with his memory completely messed up.