I kinda hate using "filler" as a word to describe anime episodes because im of the opinion that "filler" episodes are necessary to break tension and let the characters "exist" more outside of the plot but it feels like a lot of these episodes should have existed BEFORE the final Utau confrontation

Id say my favourite set of episodes are probably around ep 14 to ep 26, starting from when Nikaidou really ramps up his plans to when the first school year ends and Kukai/Nadeshiko leaves. (Though theres some episodes in that set i didnt really gaf about)