If you've ever seen a koi swim straight up to someone's hand looking for food while every other fish in the pond scatters, there's a good chance you were looking at a Chagoi. Chagoi are solid brown to olive-bronze koi, sometimes with a slight metallic sheen, and Soragoi are their gray-blue cousins, essentially the same fish with a different base tone. Neither variety is bred for a complex pattern. They're bred, and loved, for their color, their size, and above all, their temperament.
Chagoi and Soragoi are famously the tamest koi in any pond. They grow fast, often outpacing every other variety, and they tend to be the first fish to approach the surface at feeding time. Experienced keepers use that to their advantage, since a pond of nervous, newly introduced koi will often follow a confident Chagoi's lead and start feeding at the surface much sooner than they would on their own. That's not folklore, it's a real reason many breeders and pond owners keep at least one Chagoi even if it never wins a single ribbon at a show.
Both varieties trace back to the earliest days of carp farming in Niigata, long before ornamental breeding took hold, when solid brown and gray carp were simply the common food fish of the region. As Nishikigoi breeding developed, Chagoi and Soragoi were kept alongside the flashier new varieties, and over generations their size and docility became prized traits in their own right rather than something to breed away from. Today they're classified as part of the broader Kawarimono group, though most keepers just call them by name.
A quality Chagoi or Soragoi should have an even, unblemished body color with no smudging or discoloration, and the biggest, healthiest specimens can grow larger than almost any other koi variety, sometimes well past 30 inches in the right pond. For a lot of keepers, that combination of size, color, and personality makes them the fish they remember most, even in a pond full of prize-winning Kohaku.