If you use Shadow Movement to sneak into houses and a pegasus team to pull the flying sleigh... yes, in this world, it's possible to become Santa Claus! But... the Christmas tradition doesn't even exist in this world. When Rimuru tries to explain it in detail to the people of Tempest, they end up summarizing it as a "party." The Christmas cake and presents are ready, and most importantly, Kaijin and the other Dwarves create gorgeous decorations that bring the Christmas mood to Tempest. On top of that, Eren and the children treat everyone in town with their heavenly singing.
Only places like the royal capital 
throw festivals like this.
وحدها الأماكن مثل العاصمة الملكيّة 
تحتفل بمهرجانات كهذه
Nicht einmal in der Hauptstadt
des Königs gibt es solche Feste.
Este festival es propio de la capital.
Este festival es propio de la capital.
Y a que dans une cité royale
qu’on verrait tant de faste.
Feste del genere le fanno solo alla capitale.
Um festival como este não se vê
fora da capital do reino.
Такие праздники…
разве что в столицах закатывают!