So to start off, Albedo things!!
1) The flower particle in the middle of his flower is a spiral, feat my horrible diagram and no knowledge of which way it actually spirals, but you get the point.
As u can see, it's gradient from blue to white to yellow. The particles' colors are dependent on how far it is from the flower- yellow furthest away and blue closest.
2) Albedo's flower/star symbols in his moveset are oddly similar to the geo burst pulse effect.
3) Chevreuse and Charlotte share similar colors in their outfits. Another W for the Fontainian 'ch' gang :) (again this is NOT A SHIP!!! i think it's a nice color palette and interesting that the colors are similar.)
4) Xianyun really likes low back reveal for outfits, huh? You know what they say, if they like a style they stick to it. jk i made that up nobody says that (also I SWEAR I remember Xianyun's the one who also made Ganyu and Shenhe's default outfits I hope I'm not hallucinating it-)
5) In the Silken Courtyard Teapot Layout, 2D animated white cranes fly in front of the sun.
6) Fontainian weapons when held by other characters will have no special design effects, but when used by a Fontainian who has an Arkhe alignment, a specific crystal (typically teardrop-shaped) on it will have a special multicolored outline w/ either an Ousia or Pneuma special swirl around it. (Ousia outline: Blue to hot pink, Pneuma outline: Pastel purple to pale yellow. Ousia swirl: Large purple blobs with darker particles, Pneuma swirl: Almost radiating white energy with sparkles/rays of light)
7) In the Character Selection Screen, the ripples around the characters' feet actually do correlate to whether their feet are actually touching the 'ground' or not and where. This includes step ripples for entering animations that step forwards (like Chevreuse's) and jumping (like Amber's & Yoimiya's), likely also applies to other idles that have more than a minor foot position shift
Note: These screenshots are me from discord, I'm too lazy to download the images individually and paste them all here :p lol, and yes these screenshots are from my game- I am Shiirai
And that's it! I'm sorry if this counts as image spam, but I really wanted to share this :) it's really cool that the devs put in so much work to tiny details that really just kinda make the game feel well loved and as if much effort and care was put into it. Which it was! So I'm glad the details match the amount of awesomeness the team has in making this game.
What small details have you noticed about characters? Try to think of things other players wouldn't notice/haven't really taken note of ;)