The Realground, or RG, is the plane of existence that can be seen by living beings. The RG is the plane that exists just below the Underground (UG), which allows people in the UG to see people in the RG but not the other way around. To get to the RG from another plane, a being must change their frequency to match the plane. Modulator decals, which are on some shops force the beings to manifest in the RG.
Reapers, Angels, and the Composer can change their frequency to move between the planes. Reapers lose their wings and powers if they do so but the Composer can still use some of his powers which was evident in Sho Minamimoto's attempt to kill Joshua. Living beings are mostly the only people on the RG.
Even though the people of the RG cannot see those in the UG, they are still influenced by Players, Reapers, and the like. Brands become popular if Players wear them into battle. It is unknown if this applies to Reapers. People in the RG can only see people from the UG in marked shops.