If I remember correctly Nero came back and explained how he needed a new arm. Nico said she had already been working on something but couldn’t figure it out. Shortly after Nero had to deal with some demons outside of town (where he and kyrie live). They were basic so he could handle them. Nico insisted on going with him and when he saw him fighting, she got an idea for the overture from the particular demon he fought. I don’t think she used materials from it like with some of the others, but that she just got “inspiration” from it. Then she gets the idea to follow him around on his devil hunting jobs to get more ideas/inspiration. At one point she gets the idea for gerba. And then of course she gets the other ideas and materials for the new devil breakers we get in game, after watching (or from) the corresponding boss fight. I think all the deluxe edition devil breakers had a pre game story too. Like one is a Gerba prototype and I’m pretty sure sweet surrender was Nico trying to spice up Kyrie and Nero’s sex life (she might be into voyeurism and I think everyone just falls in love with Kyrie so that’s fair). Anyone’s welcome to correct me. It’s been a fat minute since I read the prequel novel summaries. Anyone’s also welcome to find the novel themselves. Just serach up Devil May cry 5 Before the nightmare. A lot of other interesting stuff (like apparently Vergil could have beaten Mundus at the end of dmc3 (so without the sparda) if he hadn’t just fought Dante; Mundus was still in a weakened state at that point. It really helped show how needless and harmful his endless pursuit for more power was. I believe that a fan group translated it and then posted summaries on social media (It’s been like a year or two since I read it in preparation for dmc 5, so I’m REALLY not sure if I’m remembering all this correctly). I think you could also find the summaries on wikia or something