Merci (メルシー, Merushī) also known as (ISDC5386292C4 Mainframe) is a computer system AI created and used by Doji, primarily in his Dark Nebula time. This computer system can speak Japanese, as well as some English and French. "Merci beaucoup" and "Très bien" seem alike to catchphrases to him and he generally addresses people in French (e.g. 'Monsieur Gingka').
For a computer system, Merci portrays a great deal of character traits. While his most characteristic aspect is his French accent, there is also notable patterns in the content of what he's saying. Merci is capable of understanding and using irony and jokes and emulates laughter when his system is hacked (it's portrayed alike to being tickled.) Usually, Merci's speech is smooth and elegant. He's polite, but his condescending speech patterns resemble those of his master.
Beyblade: Metal Fusion
Merci helped him Doji gain data on Gingka, in order to eventually completely defeat him. He made Gingka believe that he was participating in a live TV program called Challenge Blader, where he had to show his Beyblading skills. Those were then evaluated and used to the Dark Nebula's advantage.
Merci basically controls everything that is computerized in the Dark Nebula Castle, which includes every and any security function. In this function, he makes a lot of appearances. Most often he is seen chatting with Doji about recent plans.
By the end of the season, after Doji's defeat, he is forced to work for Ryuga.
Beyblade: Metal Fury
Merci's actions in this season are only revealed afterwards, in a flashback from Shogun Steel. After Doji fell down the cliff during the battle of Ryuga and Rago, Merci gets a hold of the body and keeps him alive long enough to create a digital copy of Doji's person. From then on, he lets his master live virtually as a part of his system.
Beyblade: Shogun Steel
In Beyblade: Shogun Steel is the computer system of the organization DNA. He is now featured with a new appearance, a shadowy holographic orb. Team Garcias use Merci as their computer system now. However, they have only found him and do not know that his loyalty still lies with Doji. Even the name 'DNA' was apparently picked by Merci - intended to mean 'Dark Nebula Again'.
In truth, Doji has long become a part of the Merci system and therefore Merci directs the DNA's schemes to his preference.
Even before Doji makes his reappearance, Merci betrays the Garcias by cooperating with Kira and locking them in for the duration of the Neo Battle Bladers finale.
After the tournament, Doji finally reveals his presence and Merci lets him take over interaction with the outside world.
- There is nothing said about how many sentiments Merci can simulate, but it should be noted that he is capable of misspeaking and hesitating. In the finale of Beyblade: Metal Fusion, when Doji is supposedly defeated, he still shows reluctance to address Ryuga as his master - he starts by calling him 'monsieur' and then corrects himself.