Yvoire is a serious man who claims that everything he does are for the best interests of Green Heart. He takes his job and his own ambitions very seriously and if he can't get someone to do the dirty work for him then he'll do it himself.
The party first encounter Yvoire when visiting the Leanbox Basilicom for information regarding strong monsters. He gives them a detailed map for tourists concerning areas regarding monsters, but it doesn't help them much. When they go for the second time, he is surprised to hear that they were able to defeat the monsters, but remembers hearing from the Evangelists that they were the trio going around defeating monsters. He then gives them a military map instead and says that the Basilicom may be formally requesting their help in the future.
During a conversation with Evangelist, Conversation, Yvoire is convinced by her to try and kill Neptune so that Planeptune's protection will cease which will make the residents there migrate to other lands, thus increasing their shares. He initially tries to make IF do this, but ends up doing it himself by sneaking poison into Neptune's food. He then locks them up in a holding cell beneath the Leanbox Basilicom.
When Yvoire is confronted by Vert regarding his hand in the events of the Leanbox in both the past and the present, he claims that everything he did was in her best interests. Vert takes some of the responsibility as well, saying this all happened due to her not taking her title as Console Patron Unit (CPU) seriously enough.
Hyperdimension Neptunia Re;Birth1
The party encounters Yvoire in the Leanbox Basilicom regarding information about a Key Fragment. Yvoire tells them that he doesn't know, but the Lady (Vert) might. After the group leaves, Conversation comes in. Yvoire is alarmed since Conversation is from Lowee, but Conversation tells him not to fret.
Conversation manages to convince Yvoire that the three that just came in were heretics and followers of the Overlord Momus. Yvoire is skeptical due to the girls' young appearances, but manages to convince him with Ganache providing proof with the events in Lastation. When they return, Yvoire speaks with IF privately. He tells her that while he would normally expel people, he is giving her an exception; if she kills Neptune, she can stay as a citizen of Leanbox. IF is surprised by this. Yvoire continues, giving her poison, claiming that if she is "pure", nothing will happen, and if she is "corrupted", she will die. He threatens IF with military force if she refuses.
When Neptune eats the poisoned food and collapses, Yvoire has the Basilicom staff arrest her, IF and Compa for being heretics. Vert later frees them and after curing Neptune, "speaks" with him about this. Vert seems to have left trauma on him, as Yvoire is extremely nervous when he answers her. After driving Arfoire out of Leanbox, Vert assigns Ran-Ran and Yvoire an unusually large amount of work, in which he tries to get his sleep but is unable to.
- A running gag involves Neptune or other characters mispronouncing his name, much to his own dismay.