If you mean the individual chapter, it features Tsukasa and Tsukushi getting stuck in an elevator, forcing them to spend uncomfortable alone time together.
To protect her friends from her mother-in-law's wrath, Tsukushi agrees to stop seeing Tsukasa. Hana Yori Dango Episode 21
In this version, Episode 21 is a heavy-hitter for the "soulmate" storylines and the lead-up to the finale. If you mean the individual chapter, it features
The anime version consists of 51 episodes, and Episode 21 marks a critical turning point in the F4 dynamic. "Night of Betrayal". The anime version consists of 51 episodes, and
Jan Di and Jae Kyung (Jun Pyo’s fiancée) have a heart-to-heart about their feelings for Jun Pyo. Jae Kyung is preparing to walk down the aisle, but tension peaks as it becomes clear the groom isn't ready.
While on a trip, news breaks that Shizuka (Rui’s first love) is being courted by a French politician and may marry him. Rui is devastated and tells Tsukushi that "it's over". In a moment of vulnerability on the beach, Rui kisses Tsukushi, which is witnessed by Tsukasa (Domyoji).