The remodelled form of shipgirls in Azur Lane. Retrofitting a character upgrades their stats, often adding a new skill and unlocks new character art.
From the game's anniversary artbook:
"Remodeling is to re-extract information in the mental cube and redefine it as the "presence"/"existence" of the ship, depending on experience and skill. In other words, image change. That may also lead to sudden changes in physical characteristics."
Use this when posting art of retrofitted characters.