Druids (ドルイド, doruido) are summoners who aren't affiliated with Gaia. Instead they are dedicated to protecting the Key, by conjuring and commanding familiars. The Druids have high regards and respect for nature, and for that reason they are capable of surviving in the forest, though of course there are still risks even if they are very accustomed and have adapted to it.
The only recurring character known as a druid in Rewrite is Kotori Kanbe.
Druids were once religious figures in Celtic society who practiced their beliefs secretively. They never wrote down any account of what they knew, but instead made use of a type of familiar, in the form of a mistletoe, to pass down their teachings.
They revere nature, and as such, are tasked to protect the Key, familiars created by the Earth. The nature of Salvation, however, is a taboo topic among druids, and not even the mistletoe Kotori encountered held information about it.
Unlike the summoners of Gaia, druids use the energy of the world to create familiars. Certain druids have made use of the power spot, the "umbilical cord" of the Key, to create a limitless amount of familiars and be able to control an entire forest on their own. Kotori in particular makes use of this.
They specialize particularly in the use of materials found in the forest, but knows little about animal-shaped familiars. They also make use of a variety of techniques, like creating barriers and familiars that can hide its identity. They can also create familiars that are used to pass their teachings to a suitable person, which takes the form of a mistletoe.
It is believed that they are able to resurrect the dead, however, it is very rare for a familiar to acquire a soul. Kotori assumed that the druids in the past simply thought that turning the dead into familiars is a form of resurrection, but the apparent revival of Pero and subsequently her parents challenged this thought.