syn syn syn!!!! my fellow thoma enjoyer and appreciator :3c i would like to know!! what was your first christmas like with him? were you already together? or were you both blushing and embarrassed when you realized you were standing under a mistletoe :3c
KAI! HIHI! HELLO! OH MY GOSH I LOVE THIS QUESTION!!!
Ok, so I'm going to give you two answers, because one would be when they're kids, and the other shall be when they reunite in Inazuma. ^-^
When they were kids, their first Christmas together Syn would definitely not really quite get the full concept of mistletoe, so she ends up picking it up and chasing Thoma around with it. Because aren't friends suppose to stand under it? And hug? Right? Of course when she finally catches him and one of the adults joking says they have to kiss, Thoma is completely flustered and Syn is just like, ew. I'm not kissing my best friend.
As for when they meet back up in Inazuma, their first Christmas at the Kamisato Estate would be Syn being shy the entire time and Thoma helping out. The two of them would definitely end up under the mistletoe again, only this time it would be because Ayato schemed it. They would be all flustered and shy, especially being in public, and they wouldn't be dating yet. Even still, Thoma would be the one to joking bring up when they were kids, and Syn would shyly point out that she doesn't think it's gross anymore, and then probably settle for kissing the stunned Thoma on the cheek.