Episode 20 of the anime is already known to have brought more than one Manly Tears. It doubles as a Heartwarming Moment.
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. They 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.
Taking it to a meta level, is The Legend of MomozakiP, which may be summed as thus: A fan who became famous for his contributions on NND, Momozaki Pcreated a video to promote "Tonari ni...", the image song of his favorite idol. It's a song popular among the fandom to this day, more than likely to his efforts. Fans waited for more, but a friend then reported that Momozaki P had died of a heart attack. Since then, fandom and iM@S creators alike recognized his contributions. His work has been referenced in the anime, namely the moment where Chihaya recovers her career with an acapella, later backed by the full instrumental is considered a direct reference. Episode 26 as well, which highlights a film that Azusa starred in, uses "Tonari ni..." - now think of the lyrics. A woman, mourning the loss of the man she loved. Maybe that film referred to his video, or maybe for the iM@S creators, that man in that story is a reference to MomozakiP himself.
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.
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