"COMPLEX" is a song with a similar sentiment to “I’ll BE THERE.” With acoustic instrumentation starting the track, the sound elicits another feeling of a complicated love or their “complex.” The lyrics describe reminiscing about a past lover who never leaves their mind, preventing them from being happy and finding someone new. But then there are lines like “You’re never coming back, not coming back no matter what,” and “At that time I’ll be done thinking about you,” that are used to remind themselves of the reality that they won’t be back and they have to move on, even if it’s complicated. Aside from the song, hearing the impressive high notes from Sieun’s ad-libs in the final chorus will leave you in awe of her talent and the range that STAYC has overall. 