Matthieu is an easygoing man, and pilot of the Terminus typeR606. He has a passion for music, and was a DJ prior to joining the Gekkostate. Matthieu seems to be responsible for gathering information from and maintaining contacts with lift boarders and DJs. He is also regarded as a genius. Early on, he was one of the few members of the Gekkostate who showed some sympathy for Renton Thurston although he played his fair share of jokes on him as well. Even though he was the only one to make an attempt to get Renton out of his depression over his troubles in season 2, his brutal honesty of the Gekkostate's lifestyle made things worse for Renton, and later on he felt he wouldn't do anything about it after Renton left because of Holland's control over the crew. When Renton deflected from the Gekkostate, it is revealed that he once ran away as well, as he says he believed the message Renton left them meant he wanted them to look for him after which Hap asks if he says he's talking from experience and Matthieu says he is. Although it is speculated that, like what happened to Renton, he also suffered mistreatment from Holland, who is known to react badly to changes around him. He is known to be insensitive and naïve, often leading him to be smacked by Hilda. He is also accused of being a lolicon, evident from him guessing Eureka's age based on her figure.
Towards the end of the anime, Matthieu's role becomes minimal as most LFO work is done by Holland Novak in the more effective Devilfish. Throughout the rest of the series, he is mostly taking part in battles and organizing ways to help Renton and Eureka return to the surface after helping them pass over the Great Wall.
Matthieu and Hilda often act like husband and wife, although they are clearly in a romantic relationship. Hilda orders Matthieu around as if he were her husband, and Matthieu treats Hilda as if she were his wife even though she often doesn't treat him nicely. He even calls her "honey" all the time, which she finds stupid and childish. However, they are willing to risk their lives to protect the other, which usually involves Hilda warning Matthieu of something.
- In the photo slide of Eureka Seven: The Day After, Matthieu and Hilda resigned from the Gekkostate on April 16, 12006. It is speculated that they traveled the world as ref boarders and Matthieu continued his occupation as a DJ.
- In the final chapter of the manga, he left the Gekkostate with Hilda immediately after the final battle and was last seen surfing at the new ocean with Hilda, Sturgeon, and Ruri.