Both Kim Tae-ri and Kim Ji-yeon took fencing lessons in order to prepare for their roles. Tae-ri especially later on expressed in an interview how she fell in love with the sport.
The diary of Na Hee Do in Twenty Five Twenty One drama is actually written by Kim Tae Ri while practicing Fencing with Bona. She said in a interview that while practicing with Bona she was continuously failing so she used to write down the lessons to make progress later it was used as Na Hee Do's diary .
Despite most of the main characters being in high school (Baek Yi-jin being at college age), most of the actors are far from high school age. Prior to the show's release, respectively: Kim Tae-ri being 31; Lee Joo-myung being 27 (later 28); Nam Joo-hyuk being 27; and Kim Ji-yeon being 26. Choi Hyun-wook, being the youngest, was only 19 when filming began.
Twenty Five Twenty One's ratings remain at top since it's first episode aired. Also the drama ended with 11.5% ratings and made it to the list of highest rated cable TV dramas in the history .
Kim Tae-ri's first appearance on the small screen after a hiatus of three years. She last starred in Mr. Sunshine (2018).