I don't know how long you've been a fan of JYPE girl groups, but so far as I can tell NMIXX is pretty much continuing the same pattern of success that JYPE Korean girl groups have with their debut and second songs.
- Wonder Girls (JYPE's 1st Korean girl group): Debuted with a good-but-not-great song (Irony) that followed the major music trend of the time (R&B hip hop) and achieved minor success. Then their second title track (Tell Me) went in a radically-different direction musically and conceptually (retro), and became a viral hit that spawned a national craze (Tell Me virus), leading to a string of hits.
- miss A (JYPE's 2nd Korean girl group): Debuted with a title track (Bad Girl Good Girl) that followed the major music trend of the time (sexy / female empowerment) and became known for their great performances. Ended up breaking the record for fastest time from debut to music show win (21 days), and the song went on to become the best-performing girl group song of that year (2010).
- TWICE (JYPE's 3rd Korean girl group): Debuted with a good-but-not-great song (Like Ooh Ahh) that followed the major music trend of the time (girl crush) and achieved minor success. Then their second title track (Cheer Up) went in a radically-different direction musically and conceptually (cute), and became a viral hit that spawned a national craze (Shy shy shy), leading to a string of hits.
- ITZY (JYPE's 4th Korean girl group): Debuted with a title track (Dalla Dalla) that followed the major music trend of the time (self love / girl crush again) and became known for their great performances. Ended up breaking the record for fastest time from debut to music show win (9 days), and the song went on to become the best-performing girl group song of that year (2019).
- NMIXX (JYPE's 5th Korean girl group): About to debut soon with a title track that will follow the major music trend of the time (universe lore / pastiche song structure). We'll see what kind of reception they receive, and whether they'll follow the Wonder Girls and TWICE pattern of radically changing concept for their second title track.
- NiziU (JYPE's 1st Japanese girl group) is a little different, because they got a viral hit that spawned a national craze (nawatobi / skipping rope dance) with their pre-debut song (Make You Happy). Their actual debut title track (Step and a Step) was another good-but-not great song that pretty much followed the major music trend in Japan at that time (Kpop-ified dance-centric J-pop).