This fanart depicts Flandre wearing not her regular official outfit, but rather, a crimson sailor dress with black accents and rather interesting sleeves-they are puffed at the top and flare out at around the 3/4th length (the latter aspect is perhaps a design element inspired by 18th century Western-style gowns?). It is possible that the artist has an interest in fashion, as I immediately recognized the costume in one of their many fanarts of Tanya Degurechaff from The Sage of Tanya the Evil as a homage to an outfit presented on the runway in Vivienne Westwood's 1997 Spring/Summer collection "Vive La Bagatelle".
