Believe it or not, Ed being able to turn invisible isn’t from TOH nor ITSV, it's actually inspired from an old MLP fanfic called Background Pony. It's a somewhat bleak fic but so is my work and that story has been one of my favourites for…. maybe two years now?

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While Ed had seen henna and mehndi art from time to time when growing up in Resembool, given its proximity to Ishvall, he'd only really gotten a chance to wear it once or twice in his childhood (curtesy of one of the many people who decided to watch out for the town's resident stewards).

Once William (Envy) becomes a part of his life and decides to teach Ed about their heritage, Ed is reintroduced to henna and decides that he rather likes having it. He can’t apply it himself (as he doesn’t wear the automail art by that point, although I will likely have him start sporting a prosthetic similar to what is seen in CoS) and he takes a fair amount of liberties with the medium, but it is fun.

(Yes, I am projecting. I didn’t learn about my middle eastern heritage until I was eighteen and my grandfather was literally from Lebanon.)

William gifts Ed an archeology book containing illustrations of henna art and styles, which Ed proceeds to use or inspiration whenever Kit (03 Wrath) or Nina agree to use him as a sentient canvas. Kit uses primarily floral or thermal designs (mainly vines or snow), weaving them to work with Ed's homunculus markings and spanning the length of Ed's whole arm rather than just the hand.

I'm going to talk to myself about Ed's tail and how it effects his flying. I'm doing this because I'm approaching the chapter wherein this becomes a thing for him and I need to iron out some details for myself. Posting it here makes it easier to find and archive.

So, in chapter… I want to say six of Someone, Something, and All In-Between, Ed attempts to travel by flight for the first time and finds that he can’t really turn, change directions, stop long enough to take stock of his surroundings, or land. While he is ultimately unharmed, it is implied to be an ongoing problem (later made worse by the fact that this becomes his main mode of transport).

The issue is two fold; he is fairly inexperienced with using alchemy to fiddle with air density and currents (based off of Janice the Hurricane) and he doesn’t really have a means of balance separate from his means of direction. He has wings, but those are how he keeps up and holds the currents he creates, trying to use them to change directions causes obvious problems.

Insert the tail.

He he still doesn’t have vertical stability but— do any birds? His tail offers him a way to manipulate his position relative to the current around him without adjusting the current itself (alchemy) or throwing off his balance (the wings).

As for the size of the tail feathers, when he lets them grow out they are as long and wide as a golden eagle's wingspan. That is what they are, after all; part of the chimera used on him was a golden eagle.

Big ol' birdie.

The shape and design of the tail is the same as that of the original bird; the size is of the wings. A problem then is the impracticality of having such a massive extension on a daily basis and the upkeep of those feathers. It stands to reason that Ed would keep them clipped nearly to the root until he is more adjusted and used to the tail itself, which is already quite long.

The tail to the Ed proportion is the same as for the clouded leopard used as the base of the chimera;

So it is looooong.

I've gone back and forth about the tail and eventually decided that it still has two forms (via transforming chimera magic that canon never explained) and that the default form (the long one, sweeps the ground) just grows fur and feathers at a ridiculous rate. He uses alchemy to trim the fur until it's thin and whippy, doing so at least once a month if not a few times a week, and it just keeps on growing.

Completely coincidentally, he gets some weird cravings. The materials for that fur need to come from somewhere, best to entertain the body,s fancy before a deficiency forms.