What Are Common Themes In Sans X Papyrus Ship Fanfiction Plots?

I’ve been scrolling through the Undertale tag for years now, and I’ve got to say, Sans/Papyrus stuff can be a real mixed bag. It’s definitely a more niche ship compared to the big ones like Sans/Reader or Sans/Undyne, and that almost seems to shape the themes people go for. A lot of it leans into the whole ‘brothers who have only ever had each other’ dynamic, but pushed to an extreme. You get these isolated, post-pacifist run AUs where the surface never happened, or where something went terribly wrong and they’re the only two left in the Underground. The stories often focus on dependency—how their codependency curdles into something possessive and desperate when there’s literally no one else. It’s less about romance in a traditional sense and more about exploring the cracks in their seemingly unshakeable bond when it’s all they have.

Another huge theme is guilt and atonement, usually from Sans’s side. Writers love digging into his secretive nature and the implied ‘scientist’ backstory from the game. Plots where Papyrus finds out something Sans did in a previous timeline, or experiments he was involved in, and the fallout from that. The ship then becomes a vehicle for Sans seeking forgiveness, or Papyrus trying to understand the weight his brother carries, which inevitably blurs lines. It’s angst with a capital A, often pretty heavy on the psychological drama. You don’t see a lot of fluffy coffee-shop AUs here; the tone tends to be gritty, introspective, and claustrophobic, which honestly fits the characters when you twist them that way. I’ve even seen some that blend in horror elements, playing with Sans’s powers and Papyrus’s innocent trust in really unsettling ways.

What surprises me is how rarely it’s played for pure smut. When it gets physical, it’s usually tangled up with these psychological themes—a manifestation of control, comfort, or shared despair. It’s not my personal cup of tea, but I respect how the writers committing to this ship are usually trying to dissect something specific about their relationship, for better or worse. It feels like a ship built more on character study than wish-fulfillment, which is kinda fascinating in its own dark little corner of the fandom.

Honestly, most of it just seems to take the brotherly ribbing and amplify it into full-blown romantic tension. Like, all those ‘you’re a lazybones’ and ‘nyeh heh heh!’ moments get reinterpreted as weird flirting. A common plot I’ve stumbled across is a ‘confession gone awkward’ scenario—Papyrus blurts out something he doesn’t fully understand, Sans has a minor existential crisis, and then there’s about 50k words of pining and miscommunication. It’s often way sweeter and more slapstick than you’d expect, leaning hard into Papyrus’s innocent enthusiasm crashing against Sans’s chronic apathy. Definitely a different flavor from the super dark stuff.