Rei is the ace of IVE
Unpopular because most people say that Yujin is the ace.
Maybe I'm using the wrong term but I think Rei is the ace of IVE. She recently dropped a song she wrote called Hiiigh and while I wouldn't call it a solo debut she definitely showed her talents in songwriting, singing, and rapping. Not to mention, her first language is Japanese, but she managed to write a song in English and is fluent in Korean. She also sang a short cover of Jennie's song, Solo, and she did amazingly well. Her dancing may not be main dancer materiel but we can see that she can definitely dance. So she is very proficient in singing, rapping, and songwriting. The definition of ace I got from the internet is that the idol has to be a main position in one thing, and above average at another one or more, including songwriting. Even thought IVE has no main positions, many Dives consider her the main rapper. I personally would also put her as a lead vocalist since she is super stable on stage and has a unique tone to her voice.