Christmas doesn’t quite jive with Naruto world’s culture, but there is an annual festival held in December in Nara, Japan, called the Kasuga Wakamiya On-Matsuri which I think would be a suitable winter holiday substitution that the deer summons would be involved with.
Let’s see, the festival IRL is nearly a millennia old and was meant to offer prayers to eradicate an epidemic and ask for rich harvest. Which could easily be reimagined as how the Akimichi-Nara-Yamanaka alliance becomes solidified (or changes from servitude to friendship) when the three of them came together to stop a plague and pool resources.
Seeing as how Shikako is the first full summoner in a long time (canonically, Sembei-obaasan hasn’t been able to summon Heijomaru for a while) there’s probably a role that the deer summons used to have in the festival that has gone undone for several years, or modified to use regular deer (who, while no doubt smart and friendly to people, are not as capable as sentient ninken), or human stand-in for the summons (like a chosen person wearing a ceremonial deer mask).
So I guess it’d be a lot of clan lore, a lot of world building, a lot of Shikako being trolled by Sembei-obaa and all the other elderly clan members sending the youngins off on various errands. Team Ten is also greatly trolled by the respective clan elders.
Maybe also being trolled by Heijomaru? Shikako having to keep track of Nagaoka (because as the youngest member of the Sika Tribe, he plays an important role in the festival?) which as a very excitable fawn is extremely difficult.
Basically “backstage” mishaps for the festival featuring the deer summons and clan mythology. Maybe there’s a parade through Konoha with the deer summons at the front (which I’m sure Shikako is suuuuuper fond of) except Nagaoka is missing and Heijomaru and Sembei-obaa are just watching, amused, as the youngins run around trying to find the meaning of Christmas. I mean, the meaning of friendship?
An (Almost) Relaxing Day
‘Twas the day before festival, when all through the compound,
the young leader of the parade was nowhere to be found.
His summoner searched in the village displeased,
knowing the venture would not pass with ease…
… it did not.
(No, I would not write the entire thing in that format. Just this summary. Which, embarrassingly, took me a disgusting amount of time.)