Grimdark
(TW for military, military weapons, brutality, violence)
What is Grimdark?
Grimdark is the name that Society Grimm uses to refer to a certain alternate universe version of Remnant in order to differentiate it from other Remnants. It is where Grimdark RWBY Intrvario come from. As the name implies, it has a grittier and darker overtone than canon Remnant does.
Innate Bonds
Grimdark has something referred to as innate bonds. One could accurately describe this as a soulmate function. People from Grimdark are all born with a unique symbol, known as a mark, somewhere on their bodies. This mark is typically reminiscent of something about that person, be it their appearance, personality, passion, etc. When someone meets their respective bondmate(s), their marks switch. For example, Grimdark Ruby, or Strawberry as he's called, had a strawberry mark just below his belly button. Grimdark Weiss, or Blueberry as she's called, had a small cluster of blueberries on the left side of her neck. When they met, their marks switched. Strawberry then had a small cluster of blueberries just below his belly button, and Blueberry then had a strawberry on the left side of her neck. This is how bonders know when they've met their bondmate(s).
Appearance Differences
People from Grimdark look different from their canon counterparts in noticeable ways. It isn't always in the same ways, depending on certain aspects of the person's appearance and the significance of certain things, but typically speaking, it is usually safe to assume that their hair and eye colors are reversed. Outliers of this include, so far, Strawberry, Yang and Blake. Strawberry's hair is reversed only in the way that it's primarily red with black ombre, as opposed to his canon counterpart having primarily black with red ombre. His eyes are still silver. Yang's hair is orange, and his eyes are black. We believe this is due to his reincarnation type of link to Blake. Canon Yang's eyes are the same color as canon Blake's soul. Therefore, with colors reversed, Grimdark Yang's eyes are black to match Grimdark Blake's reversed colors and soul. Blake's hair is purple, and her eyes are orange due to the same thing regarding Grimdark Yang's appearance. With all other people from Grimdark, so far, they have just had reversed hair and eye color due to the reversal of their color allusions.
Lore
The main fork in Grimdark history that changed the entire timeline happened when Strawberry was just a child.
Instead of only his mother dying, his father also died.
Team STRQ was on a very important mission together (details of which were not ever shared), and half of their team was killed, which led to a large cascade of panic and fear that the Atlas military took advantage of.
Huntsmen were abolished, teams disbanded, and the academies were turned into military training operations to dole out new recruits under the Atlas military control.
Safe cities were set up around Remnant, where citizens stayed. Outside of these safe cities, the land was near barren. Drone strikes, firebombing, raids, these were all common things to happen outside the borders of the safe cities, so it was extremely important for people to stay within the bounds. Or face decimation in the constant struggle to fight off the Grimm.
Life in Grimdark was a constant struggle, looking over your shoulder, danger around every corner, an ever-looming threat, from not only Grimm, but other people and the military that had control over the entire world, except Menagerie.
Menagerie was where the Red Claw militia was stationed, a rebel force that fought back against total military control and held their ground, though that's all they were able to do at the time.