Game takes this long, like after chapter 3 is when challenge actually starts to kick in. Ballet Twin boss, at least for me first try at Hollow Zone mission Skyscraper. I'd recommend not underestimate any shield bonus Resonance in that mission and also try not to reach 5 corruption, last corruption means boss dealing 40% damage more.
This mission is somewhat annoying, the main mechanic is trading entire team HP for bonuses or worse, negative effect.
Check any new Hollow zone tier mission, try to have first time completion for 600xp to Inter-Knot level.
Maybe a bit non-major plot spoilery, Idk if anyone has Soldier 11 or not, her trust level up (3) mission where you are supposed to find a lot "top secret" document.
I didn't manage to screenshot the top secret document text dialogue. Apparently, S11's commander has a
robot daughter and quite popular on TV as implied in the document. So the
daughter may or may not be one of idol girls.
I may misread while clicking through dialogue, I could be wrong.