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.
Santa Claus only comes to 
kids who have been good!
!سانتا كلوز لا يأتي إلّا للأطفال الجيّدين
aber der Weihnachtsmann
kommt nur zu braven Kindern.
pero Santa Claus solo visita
a los niños buenos.
pero Santa Claus solo visita
a los niños buenos.
mais le père Noël ne rend visite
qu’aux enfants sages.
ma Babbo Natale si presenta 
solo nelle case dei bravi bambini!
O Papai Noel só visita
as crianças boazinhas!
но старичок Санта-Клаус приходит
только к хорошим детишкам!