is passion related to passion raga??? i dont understand

Passion raga is xinlu's story

Raga is a spinoff of Passion.

Exactly, Passion is the main story of Taeui, Ilay and various shenanigans in which Xinlu and Yuri Gable are involved. Passion Raga is the side story of what happens with them after Taeui, for a lack of better word that doesn't spoil events from Passion, gets to know Rahman (who I'm pretty sure will have his own side story with another important character that shows up in Passion raga)