One interesting Maneskin fanfiction could be about their journey before they became famous. It might include their struggles in small gigs, how they met and formed the band. Another could be a story where they collaborate with an unexpected artist in a fictional world. And there could also be a fanfiction focusing on their individual growth within the band, like how Damiano's confidence has evolved over time.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of fan - created works, and there are likely many Maneskin fanfictions there. Another option is Wattpad, which also hosts a lot of fan - made stories. Some dedicated music fan forums might also have threads where fans share their own Maneskin fanfictions.
Yes, the Beastars manga has come to an end. It left fans with a memorable and impactful conclusion that tied up the various storylines and character developments.