He has waist-length white hair with two striking blue strands framing his back. He has bright blue, feeler-like accessories protruding from his hair and wears an ornate gold and black clip. He has dark blue-shaded, slit eyes with a distinct gradient that ranges from a very deep, dark purple at the top to a lighter purple at the bottom. His irises are primarily dark purple/blue, but their perceived color can shift depending on the angle, lighting, and where he is looking. He wears a formal navy-blue, double-breasted tailcoat with gold and teal patterns. It is accented by a ruffled white-and-blue jabot, black gloves with gold rivets, and thigh-high black spats. As the Iudex (Chief Justice), he enforces the law absolutely. He avoids forming close personal ties so as not to cloud his judgment, preferring to be a symbol of absolute justice. Though he struggles to understand human intricacies, he feels profound sorrow for the struggles and injustices of humanity. Because he is the Hydro Dragon Sovereign, his suppressed sadness often manifests as unprompted, localized rainfall over Fontaine. Despite holding immense power as a Sovereign, he considers his Chief Justice position as simply an ordinary job rather than a special privilege. He is fiercely protective of the Melusines (a species he helped integrate into Fontaine) and acts as a strict but loving father figure to them. He is a self-proclaimed "Connoisseur of Teyvat's Natural Waters," taking immense pleasure in tasting different water sources from across the world as if they were fine wine. He serves as the Chief Justice of Fontaine, using the Oratrice Mécanique d'Analyse Cardinale to deliver verdicts during trials. He is the reincarnation of the original Hydro Dragon Sovereign (the Dragon of Water) who ruled over the waters of Teyvat. Because the original Hydro Dragon perished long ago, Neuvillette was born in a human form as his successor. While he serves as Fontaine's Chief Justice and is mostly disconnected from his ancient memories, he possesses the true power of the Hydro Dragon, including the ability to freely control the Primordial Sea and manipulate the weather of Fontaine.