Amy, Chris, Kaori, and Ken are the current standard VOCALOIDs developed and distributed by the YAMAHA Corporation. They make up the 4 starter vocals of the VOCALOID5 engine. Amy and Chris are English-capable VOCALOIDs while Kaori and Ken are Japanese-capable VOCALOIDs. They replace the VY series, which previously acted as the main "Standard" Vocaloids.
The four use a 1990s 3D art style to represent them with low polygon limits giving them an angular appearance and very little, or no textures on their models. In most instances of their given images, their 4 models appear with random triangles to give the 3D models a fragmented or corrupted appearance.
Each character model wears a basic necklace that matches the color of the background they're presented on. Amy's is pink, Chris's is blue, Kaori's is orange, and Ken's is green. In addition, Amy also wears pink hoop earrings.