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.
You get things like a fir tree, 
cake, turkey, and presents...
ومن مظاهرِه شجرة التنّوب والكعك
...والدّيك الرّومي والهدايا
Man stellt einen Tannenbaum auf, backt Kuchen,
isst Truthahn und schenkt Geschenke.
On décore des sapins,
on fait des gâteaux,
Si preparano gli alberi di abete, la torta, 
il pollo fritto speziato, i regali e poi...
Preparamos pinheiros, bolos, perus,
На этот праздник готовят ёлочку там,
подарочки всякие, ну и индюшку у нас…