The Oyama brothers (Japanese: 大山兄弟 Romaji: Ōyama Kyōdai) are a playable character type in Double Dragon 3: The Rosetta Stone. They are instructors of a martial art known as Seishin Karate (成真カラテ), capable of delivering speedy attacks. Their special technique is the Overhead Collar Throw (Japanese: 猛虎回派山 Romaji: Mōko Kai Ha Zan).
In the export versions of Double Dragon 3, players can only play as an Oyama brother by purchasing the "Extra Guys" option from the item shop in the beginning of Mission 3 (Japan). They become playable after the player's current character is killed. In the Japanese version they're selectable from the start.
- Masao - The first Oyama brother, who dresses in a white karate gi.
- Kunio - The second Oyama brother, who dresses in a red karate gi.
- Akira - The third Oyama brother, who dresses in a yellow karate gi.
- The Oyama brothers appear to be modeled after real life martial artist Mas Oyama, founder of the Kyokushin school of Karate.
- Masao was originally supposed to be only Oyama brother in the game. The other two, Kunio and Akira, were later added to allow multiple players to control the same character type.
- Masao's original name was going to be Masahiko according to unused graphic assets showing his full name in kanji (正彦 大山). It was shortened to Masao, presumably due to the name display under the player's health gauge having a five character limit, as every playable character in Double Dragon 3 has a name that fits this limit (e.g. Billy, Roney, Seime).
- Kunio, the second Oyama brother, shares his name with the high school delinquent protagonist from Technos Japan's own Nekketsu series, which was the company's other popular franchise in Japan. However, the Kunio from the Nekketsu series has no official surname.