Fewer arbitrary constraints on creativity
In Dice-Paper-Story, many of the basic elements of current roleplaying games will be removed, to make way for other elements of roleplay.
No classes. Your character gets defined by their background experience and the choices they make in gameplay.
No levels. Characters gain “notches” of experience in each skill they attempt to use.
No Armor Class. Characters have a Dodge Score and Damage Absorption from armor.
Probably no Hit Points. During an attack, you (or foes) get hit in various body parts. A high enough score crushes or severs that part. Fights are short and generally avoided, because permanent maiming or bleeding-out can occur. The Boromir Death Scene is possible in this game system, whereas it really is not in most d20 systems.
Realistic constraints to make interesting roleplay
Characters start very poor. Prevailing wages are 2 silver per week. Adventure rewards are also slim, typically 10 gold per person. ‘Class’ really does matter in D-P-S, but it is ‘class’ as understood in the real world. Inequality is a powerful basis for roleplay. Characters may need to engage in hard negotiations for better pay, better jobs.
Characters cannot be armed nor armored in urban public spaces such as streets, shops, and taverns. Important roleplay questions: When do they decide to armor-up? When do they decide to buckle on sheathes and holsters? When do they decide to draw blades?
Pay attention to encumbrance. Why? So that characters must carefully choose what they will carry with them.
Spells are difficult to obtain. Even if you can cast many spells per day, you may have great difficulty finding copies of any spells. A lot of roleplay can be about finding and copying spells.
All Spells require a Material Component, which might be difficult to obtain. Lots of roleplay potential about why you want to buy small bits of cooper wire, owl feathers, bat wings, or eye of newt.
All Spells need to be cast by expressing a phrase. Preferably a dialect of Avestan, Kiswahili, Icelandic, Quechua, Sanskrit, Mayan, or Tuareg. At session zero, player declares which language they will use. Different players in the same party could spellcast using different languages. The take-away is that players have to start learning a pretty unusual language.
Messages will be written in a different writing system (but in the language you all know at the table). Choose from Georgian, Armenian, Ge’ez (Ethiopian), Tifinagh (Berber), Devanagari (including any of its variants such as Malayalam, Thai, Cham, Gujarati), or one of the Runic scripts: Futhorc, Futhark, or Orkhon Turkic. Players and the GM just need to agree which script will be used at the beginning of the campaign. For glyphs, I would use Hanzi (Chinese characters, either Traditional or Simplified) or Maya logograms. Each of these scripts are beautiful and brilliant designs, with deep aesthetic richness, and players and GMs benefit from learning any of them.
Cosmopolitanism rather than exploitation of the ‘exotic’
The two last constraints–spellcasting language and writing systems–could veer towards an exploitation of the exotic. I have already written against the implicit colonialism of old-school RPGs. I also encourage listening to Three Black Halflings for a more in-depth (and humor-filled) critique of colonialism and exploitation of exoticness. The intention here is the opposite of exploitation: it is to respectfully introduce us all to the diversity, creativity, and beauty of different cultures. Learning the Georgian Mkhedruli script certainly is not an in-depth lesson in cultures of the Caucasus; that would take decades. However this little taste of Kavkaz (or Berber, or Norse) culture might trigger that deeper interest and study. Furthermore, it immediately reveals non-Anglo design creativity on very specific terms: through Player usage. The Three Black Halflings want more drums (and less lute) in roleplaying, because they want more representation of various African cultures as the protagonists, as the agents of action in the story. Amen.