• English / United States: Steven Stone
• Japanese / Japan: ツワブキ ダイゴ
• Japanese (Romanized) / Japan: Tsuwabuki Daigo
• Japanese (TL) / Japan: Tsuwabuki Daigo

Steven is the son of the president of the Devon Corporation. Steven is also the Elite Four Champion in the Houen Region.

Studying Mega Evolution

Since his encounters with Ash Ketchum and his friends, Steven Stone spent his time traveling and looking for various stones and ever since he came to know of the existence of Mega Evolution, he has been searching for its roots. He found a piece of a wooden plate that had been divided with each have differing contents. He combined his piece with the one that Lysandre had found and discovered that according to the wooden plate, the ancient people in the area of the Hoeun region owned a legendary megalith. The text was deciphered by Steven and stated: "The path to the megalith begins with the gate. The key to opening the gate is the glimmer of two stones. When those stones come together, a new path will appear."

Steven Stone had been researching in the area and he along with Alain, used their Mega Stones to open a path to the top of a mountain where an ancient city ruins was located. There they discovered the megalith which disappeared after an encounter with Mega Rayquaza. Having detected undulation that matched the megalith on the coast of Kanazumi City, Steven Stone went with Alain and Mairin to investigate.