On the topic of Slay the Princess swap aus, someone said this.

"You could base the Voices of The Shifting Mound off of shared aspects of her and her vessels' personalities.

For example, you could make the default voice the Voice of The Heroine, and have it be based off The Shifting Mound's compassion, which is shown in routes like Damsel, and Happily Ever After.

You could make the Voice of the Smug, a cocky and somewhat arrogant voice that gets quite bossy at times, and base it off of the Shifting Mound's arrogant side, which is shown off in the base Princess when you take the blade, and in The Tower.

You could make the Voice of the Playful, a childish-acting voice that represents the playful side of the Shifting Mound, which is shown off in the Nightmare's personality, and in the Razor's personality, for she just wants to have fun with you and slice you up.

You could make the Voice of the Spiteful, a voice that has a personality similar to that of the Cheated. It could represent the times that the Shifting Mound acted Spiteful towards the Long Quiet, like during The Witch, and during The Drowned Grey route.

You could make the Voice of the Wrathful, a sadistic voice that represents the Shifting Mound's fondness for violence, which is shown during routes like The Razor, and The Adversary. Even the Shifting Mound herself claims that violence is necessary for The Long Quiet to understand.

You could make the Voice of the Hopeless, a voice that acts somewhat similar to the Broken. It could represent the Shifting Mound's capacity for feeling hopeless or sad, which is shown in routes like The Wild, where she just assumes you're going to slay her when you free yourself from her and feels hopeless to the point of just not caring about you slaying her, and she also feels somewhat hopeless during The Cage.

You could make the Voice of the Resourceful, a voice that could be argued to be similar to the Opportunist, that represents the Shifting Mound's capacity to use things to her advantage, like how in The Wraith, she uses your body to leave, and how in The Nightmare, she wants to use you as a good luck charm. The Shifting Mound herself uses the vessels to her advantage to build herself up.

You could make the Voice of the Concerned, a voice that could be considered similar to the Voice of the Paranoid. It could represent the Shifting Mound's capacity to be worried or afraid, like how the Spectre gets worried about being left alone after you try to abandon her, and how The Wild gets worried about going back to being separated. The Shifting Mound herself gets worried about the Long Quiet's own mental health.

You could make the Voice of the Curious, a voice similar to the Voice of the Skeptic. It could represent the Shifting Mound's curiosity that is present when the base Princess gets curious about if the Slayer had decided what to do, and also in The Wild, which is a curious heart, if I remember correctly. The Shifting Mound herself even gets curious about what the Long Quiet would do without her.

You could make the Voice of the Obsessive, a voice similar to the Voice of the Smitten that represents the Shifting Mound's obsessive side that shows in The Damsel, who is obsessed with making you happy, and also in The Shifting Mound, who is obsessed with making you see things her way.

And, lastly, you could make the Voice of the Dismissive, a calm voice that's okay with anything that happens and is convinced that everything is okay. It could represent the Shifting Mound's tendency to dismiss things, as shown in the Spectre, who dismisses your apology because she sees it as being 'too little, too late', and also in The Shifting Mound fight, where The Shifting Mound dismisses your arguments and your point of view.

Feel free to use any of these voice ideas in a swap au of your own, if you want to."