Sasaki is the older brother of Runa Sasaki. He is also Yamada-kun's senpai back in their hometown. His hobby is playing video games. He also plays the game Forest of Savior (FOS) and is also a member of the guild [Chocolate Rabbit].

Spoiler

He is the current guild master of [Chocolate Rabbit] under the name: Princess Ruri. He is a nekama. (Nekama : a male who dresses as a female, and uses anonymity in his social network with his appearance and identity unknown. It is an abbreviation of the word 'netto okama' where it has been used since the pre-internet online service era)