Chara and Papyrus is such a weirdly wholesome dynamic if you think about it? Like, one's the embodiment of chaotic violence and the other is the purest skeleton who just wants a friend. A concept I keep coming back to is them getting stuck together somehow after a reset glitch—Papyrus remembering just enough to be confused, Chara being their usual creepy self but weirdly disarmed by his relentless, unconditional friendliness.
Maybe it starts as a kind of psychological horror where Chara is just playing along, waiting for the perfect moment to shatter Papyrus's worldview, but the sheer, stubborn force of his niceness starts to... work? The real drama wouldn't be about redemption exactly, but about Chara facing something their determination can't overcome: a kindness that refuses to break. The setting practically writes itself—forced proximity in Snowdin, Papyrus trying to teach them puzzle etiquette, Chara begrudgingly finding Sans's terrible jokes less irritating when filtered through his brother's earnest laughter.
You could even flip it: a timeline where Papyrus, through some anomaly, is the only one who can perceive Chara's ghostly presence post-pacifist run. He'd just assume they're a new invisible friend who needs cheering up, narrating his entire day to them, trying to knit them a sweater. Chara, who expects fear or anger, is instead met with a baffling, one-sided friendship they can't escape. The horror becomes a different flavor—not of being hunted, but of being truly seen and accepted by the one soul you feel least deserving of it.