I have a question. Experienced players, please help.

I'm a beginner who started playing about a year ago. I originally recorded the anime 'Dererani' during its rerun period and watched it all last year. That's what inspired me to start 'Dereresta' as well. I haven't played all the songs yet, but I'm having fun. So, to the main point. I don't quite understand since I got into it through the anime, but there are anime songs within the live performances, right? Most of the unit songs are not in the regular song list! They are in Master+, was it? They are there. Also, during special events, they are unlocked within the event. It seems the easier versions are only available during those events, and I can't find them anywhere else. Is there a solution? Do I just have to wait for the next event? I know that collaboration songs were removed last year, but I don't know about the anime songs. Experienced players, please help me out.