To steal a purple soul (And hold it gently in your hands)

To hold admiration towards a man who never interacted with anyone was foolish. To want to get closer to him despite knowing what he's capable of was even more so. But was it truly so foolish if her devotion was eventually noticed? Perhaps the reclusive man held more in his heart than cold calculations, if only for one person. One woman, who managed to steal his soul and held it gently despite his crimes.

Or: Reader is determined to help in any way she can and manages to slowly slip through XGaster's walls and into his soul. Neither knows what to do and is too blind to notice the pining. XAlphys and Ink are amused, until they aren't.