Episode 22 is a rather bittersweet moment as all the idols meet up for Christmas, but knowing that they'll see each other less and less as time goes on.
Episode 23 has the ever-cheerful Haruka almost breaking as she is forced to practice and rehearse all alone, as everyone else is too busy to join her.
Episode 24 - Haruka's acting on the audition for the musical. In 23, the director was deciding on whether Miki or Haruka would play the lead role, about a dramatic, morose character grieving over the loss of her comrades, and who would play the supporting lead. 24 reveals that Haruka got the lead because she was going through that exact problem at the time, and used it to channel her performance!
Later in the same episode, when she basically cheered herself up and the whole gang calls out to her during the commercial announcing their next live. The announce that they'll "be waiting for her", and she races toward the office...
The "Last Concert": if you fail to garner enough fans for your idol, 765 decides to terminate her contract. You then have to give her the bad news and book her farewell concert. As for songs,Tonari ni.
Of note is that, as attendees in the comments have pointed out, Asami Imai is among the most experienced singers of the group, so her breakdown was a shock to the other ladies. Both on stage, and in the audience, everyone sang in her stead.