Miyuki Nakayama, the author of Blend S manga, posted an illustration to celebrate a character's birthday from the manga.
The character, Mafuyu Hoshikawa, plays a role of "Sister" at a cafe, Stile in the anime.
December 23rd is her birthday.
Blend S is an airing anime for Fall 2017.
The manga has been serialized in Manga Time Kirara Carat.
The manga's 4th volume was released on October 27th, 2017.
Via - Official Twitter Account: