HG (High Grade) and RG (Real Grade) are two different grades of Gundam model kits. HG kits are generally more affordable and easier to build, while RG kits are known for their exceptional detail and complexity, closely resembling smaller versions of Master Grade kits. RG kits typically feature more parts, greater color separation, and better articulation compared to HG kits. However, this also means that RG kits can be more challenging and time-consuming to build.