Definitely Sakuya, the hair is a giveaway. Tagging her boldly...
hang on a minute, could be Flan too, pillow blocks the ponytail side of her head! Can someone verify from Pixiv?
Nothing on it from pixiv, but given that Space jin tends to draw ponytails starting higher up on than could be hidden by the pillow, Flan is unlikely. Also he tends to draw Remi with slightly shorter hair than this.
I'm tagging it Sakuya, the context of the Sakuya X Meiling meme and all other evidence considered.