Dex Oyama, known as Dekao Ooyama (大山 デカオ) in Japan and Dex Ogreon in English anime and manga, is a character from the Mega Man Battle Network series. He is Lan's rival and GutsMan.EXE's operator. He has a little brother named Chisao, that believes that Dex is the best NetOp in the world; and Dex tries desperately to maintain his respect.
Although his skill never quite allows him to defeat Lan, he is nonetheless a dedicated Netbattler who frequently ranks highly in several competitions and provides key assistance in a handful of incidents.
Dex acts very arrogant and boastful. He cares very much for Chisao, often panicking when he gets in trouble, and tries to maintain his respect in both the games and the anime. He also has a rivalry with Lan and the two compete whenever they can, usually by Netbattling.
He and Lan are similar in that they forget to do homework and do poorly in class. Dex also gets very mad when Mayl hugs Lan or shows any kind of affection for him at all. Dex cares deeply for his friends and is willing to risk his life for them. Dex has also been known to get emotional, like when he was going to move away to Netopia.
Dex and GutsMan can be fought in every game up to Mega Man Battle Network 4 for his chips. He often takes part in Lan's adventures, assisting him and sometimes needing to be rescued. Dex moves away to Netopia in Mega Man Battle Network 3, but returns later to help Lan fight the WWW. He appears to cheer Lan on during many occasions and to hang out with him. Dex also provides some humor in Mega Man Battle Network 5 by displaying the Houdini of the beach. In Mega Man Battle Network 6, it is revealed that he becomes mayor of ACDC Town in the future.
Like in the games, Dex is Lan's rival. Prior to the series, Dex always defeated Lan in NetBattles; but, after Lan's generic NetNavi is upgraded to MegaMan.EXE, he is easily defeated. Dex provides comic relief in many episodes. Once, he was taken to the hospital because a robotic cat bit his leg and wouldn't come off (and his hurt leg was repeatedly struck, either by dropping onto a surface or being bit again). He also has a crush on Mayl, but is always turned down. He enters the N1 Grand Prix, but is defeated.
In Axess, he goes to another country with the ex-WWW members to work at their curry shop called Number 2 Curry and train hard. When he comes back, he has a gung ho attitude and challenges Lan and MegaMan to a Netbattle. However, they are attacked by BurnerMan.EXE and MegaMan teams up with GutsMan to defeat him.
In later series, he continues to work at the curry shop, both as a cook and as a delivery boy, until moving back to work at Number 1 Curry. His appearances are less frequent compared to previous series.
- He is fond of action and shooting games.
- Dex is good at Chess.
- Dex's Japanese name (Dekao) includes the Japanese word 'dekai' which means 'huge', while his brother's Japanese name (Chisao) includes 'chiisai' which means 'small'.
- Dex is one of the only two characters to actually attempt to use Cross Fusion, but fail to do so. The other was the Cross Fusion Test Volunteer in episode 1 of Axess.