Kind of stupid. Celica can't unlock her power without Nel taking over, once again proving that Nel is the real protagonist of the game. It's getting kind of pathetic that Celica is really a background character.
With the new Violet events we once more see that the author really likes going into an unusal "subby hero" direction. It's something new and different.
You can reinterpret this as Celica lacking the natural Celestian mindset (though she can take iron-asscheeks-form without Nel after the first time), but her strength will lie in her allies.
When that edgelord guildmaster finally reveals himself to have been the demon king all along, all the allies Celica will have honeytrapped will descend and kick his face in.
Anyone able to unlock last 3 Nel events?
These are the last three Nel events - 25 was an on-wakeup-event, so just have your Nel relationship maxed and progress the story, the other two happen in the hot springs as the story progresses.
If you are missing others, well, one would have to know which ones.