Throh is a bipedal, humanoid Pokémon with a bulky, red body and rocky skin. Its head is round and low on its shoulders with a T-shaped black feature that forms its nose and brow. Its hands and feet each have three digits, with its fingers being rounded. It wears a white judogi with a black, v-neck collar that extends down to its black belt. The gi has an integrated diamond pattern on its sleeves and a black, square patch on the bend of its knees. Throh is a male-only species.
Throh travel and train in packs consisting of five members. Any member of the group that cannot keep up will throw away their belt and leave the group. It weaves its black belt from vines and ties the belt to increase its power. The belt grows darker as it absorbs more of Throh's sweat. It is driven to throw larger opponents and will always try to do so.
According to interviews with Ken Sugimori in Nintendo Dream, Throh draws inspiration from martial arts that involve throwing, and notably a judoka (a judo practitioner).
During development, Throh and Sawk both had horns, which may hint towards their design being originally based on oni. However, they were replaced with eyebrows so as not to clash with Tornadus and Thundurus, who were originally designed to be red and blue, like Throh and Sawk.
It may also draw inspiration from namahage, demons wearing oni masks, replacing the mino with a judogi.
Throh may be derived from throw.
Nageki may be a combination of 投げる nageru (to throw), 撃 geki (strike), and 鬼 ki (demon).