As one of the pixiv comments points out, the dakuten above the "す" is shaped like an "い", thus making it spell "めリい くリすます", a more accurate spelling of "Merry Christmas".

Just another year of tsundere Santa kasumi giving gifts. No wonder she gets picked.

halseyttk said:

As one of the pixiv comments points out, the dakuten above the "す" is shaped like an "い", thus making it spell "めリい くリすます", a more accurate spelling of "Merry Christmas".

That's ridiculously clever w