アルルさん
#ぷよの日
This is due to a Japanese goroawase (pun based on numbers' readings), where "2" can be read as "pu" (ぷ) and "4" as "yo" (よ), making "pu-yo" (ぷよ). On this day, social media (SNS) in Japan gets really lively with topics and posts about Puyo Puyo (the popular puzzle game series).
