Whenever a musician participates in the writing of song composition, lyrics, or arrangement, the Korea Music Copyright Association (KOMCA) puts it on their records.
Here are the top 80 idol song-writers on the KOMCA list with the most number of copyrights under their name as of 15th June 2021.
PS: Writing a whole song and writing a verse in the song is different cases. But KOMCA does not separate these two situations. Both cases count one as royalties on KOMCA. Therefore, all of the copyright-related lists are mixed like above. As the maker of the list, I can say that the most of the rappers on the list -not all but most- just write their own verses.