The original "after-school casual" default costume of Nijisanji's Uzuki Kou, as seen in post #6676345. He used this from June 2018 to February 2020 when his school uniform became his current default.
It consists of a short-sleeved blue plaid jacket that is white at the bottom. He wears a long-sleeved grey undershirt, which is typically visible under his jacket.
This tag implicates uzuki_kou (learn more).