Is this a skill that defines the character? Is it something that you can imagine them without? Aurin is probably the most hypersexual character I've ever played. It stems from trauma (doesn't it always?) that I've explored somewhat in historical solos that I'm continuing to write when I have the time and inspiration to write solos. His job when I created him (omg, over 4 years ago now) was managing the Velvet Cabaret. While not officially a courtesan himself, he did his fair share of seduction, whether that led to sex with him using the promise of it as currency or collateral. He's not great at platonic friendship and has on more than one occasion gotten himself into trouble for using seduction when it wasn't the correct tool.
How often do they use the skill? If it is something used infrequently, it is likely not a candidate for Grandmaster. I would say he uses it everyday. He seduces people, brings them into the fold either to work for him as informants for Portions for Foxes, and a lot of the drama attached to him involves him seducing people and then having to deal with the ones who stick around and want more from him. He's already a Master, so clearly he has been using it with some regularity.
What efforts has the character put into developing their own perspective and unique approach to using the skill? What is their trademark use of it? His youth trained him to weaponize everything, including sexuality. Seduction, whether sex is the end game or not, is just a tool to get what he wants out of a person or a situation. If he's good at actual sex, it's because he focuses on figuring out what a person desires and giving it to them. This skill is actually being sharpened because he seduced a Moritasi of Desire, Eshar, and his "style" just naturally reflects theirs. I've tried to play him as having keen emotional intelligence when it comes to a mark, and less so self-awareness.
Is this a skill that others immediately attribute to the character? If not, consider fostering a reputation involving its use. He certainly has a reputation for being a slut. Whether people would say he has a reputation specifically for the seduction... you would have to ask them. I would say yes, but... see below.
How have you used the skill in your writing to impact not just your own character but others? He's seduced several PCs that he recognized something of himself in: Arvalyn; Torin; Castor; Rivin. He's seduced PCs just for fun: Hilana. He's pity-fucked PCs: Korvaelis, which led to an oops! There have been seductions that didn't lead to sex, but he's using the skills: Brenner; Aurelio; Reiner. And all the NPCs... He banged the former impresario of the Golden Peacock as part of the maneuvering that got him her job. I promise this is not just an attempt to get Imogen and Carina into bed.
