Hey, Lust and sexual deviancy are two different things. Lust isn't always sex and banging everyone, it's not carnal pleasure, it's the emotional value of it. People associate sex with things like love because typically, you don't have sex with people you don't love (It's why rape is so horrible since you're forcing someone to love you against their will). And yes, Fran is a succubus so normally she would exploit the physical lust most people would have, such as enticing young virgin men (Read: nerds) into having sex with her under the impression that someone like them could "attract" the love of someone like Fran.

But with that being said, Fran herself has no real need for lust. The sex is just something she likes to do, like killing people with her axe, which you might thinks is a wrath thing. No, if anything, Fran's sin is Sloth. She has at least half as much potential as a succubus as VIctoire does, but her sloth, or in other words her own laziness and preference for simple pleasures, has prevented her from even using some of a succubi more iconic powers such as high level illusions, shapeshifting, or life stealing. Fran's sin is that she's too lazy to actually improve herself and wastes her time fucking around, literally.