Idol Jihen

Both of these shows throw plot out the window. They have vague reasons why the large groups of girls are important, but don't let those 5 minutes of explanatons fool you: They're about getting a dozen or so anime girls together to do cute things and that's it. They're 80% 'filler' 

Both have idols, but this is politics with singing.  

Both animes are allusions to social organizations: in Idol Jihen, the idol groups are political parties, while in Akiba Meido Sensou, Akiba's maids are mafia groups. They fulfill the obligations/adhere to the rules of their organizations. 

Both animes talk about idols helping other people. In Idol Jihen groups are political parties. They solve urban problems. In Zombieland Saga already dead idols in the form of live zombies help people from their past. The main characters of both animes overcome their difficulties and failures.  

- Idols are to fight against something by singing and dancing - Both try to be serious about something being hostile against the idols (just that one fails terribly) - Both main characters (Nagisa & Natsuki) show the same kind of personality traits