Regu is a robot who appears to be a little boy. His actual age, origins and even name are unknown since he can't recall anything about his life before the encounter with Riko. He was named Regu by Riko after a dog she used to have.

Regu's body is extremely durable and resistant to physical damage, it's also way lighter than its size would suggest. The arms could be extended for as far as 40 meters and each of them has a built-in Incinerator relic. These high-powered beam cannons are capable of reducing to ashes almost anything, however Incinerators are weapons of last resort since even a single shot depletes the body's energy almost completely making Regu lose consciousness for a few hours. Having an artificial body Regu might be the only thinking being completely immune to the Curse of the Abyss, because of that he is sometimes referred to as "The Treasure of the Deep."

Despite being a formidable fighter Regu is rather shy and unassertive. He blushes easily and often cries when in distress. Unlike Riko, Regu is easily flustered by danger and has to rely on Riko's judgement in difficult situations.