Water-borne coating composition set and multilayer-coating-film forming method using same

A water-borne coating composition set for forming a multilayer coating film having a first base coating film and a second base coating film,

• the water-borne coating composition set comprising a first base coating composition that forms the first base coating film and a second base coating composition that forms the second base coating film, wherein
• the first base coating composition comprises a first coating film-forming resin, a first curing agent, a first inorganic brightener, and a first hydrophobic association rheology control agent,
• the first inorganic brightener is at least one selected from the group consisting of silica, talc, calcium carbonate, kaolin, barium sulfate, and diatomaceous earth,
• the second base coating composition comprises a second coating film-forming resin, a second curing agent, a second luster material, a second inorganic rheology control agent, a second hydrophobic association rheology control agent, and a second dispersant,
• the second inorganic rheology control agent comprises a layered material having a stacked structure of inorganic crystal layers,
• a nonvolatile content NV1 in the first base coating composition is 10% or more and 45% or less,
• a nonvolatile content NV2 in the second base coating composition is 3% or more and 17% or less, and
• the nonvolatile content NV1 is greater than the nonvolatile content NV2.