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.
Incidentally, this is for a gag 
we will perform for Great Rimuru.
بالمناسبة، هذا لمسرحيّة فكاهيّة
سنؤدّيها لأجل ريمورو-ساما
Das habe ich mir übrigens ausgedacht,
um Meister Rimuru zu überraschen.
Son para hacer reír al señor Rimuru.
Son para hacer reír al señor Rimuru.
C’est un accessoire pour un numéro
destiné à maître Limule.
Comunque, useremo questo oggetto
Isto é para uma piada de impacto
que Rimuru-sama quer apresentar.
Кстати говоря, это очки для фокуса,
что мы покажем Великому.