Specific moments occur in episode 42, where, after becoming an Idol Singer, overcoming hardships and traveling to America to find him, Mitsuki finds that her childhood friend Eichi died a year and a half ago. This is either better or worse in the manga, in which Eichi died in a plane crash and Mitsuki knew from the very beginning that he was dead, but was in serious denial and became Full Moon to find him anyway.
Then there's the last episode, where you can cry in despair for the first half and in happiness for the second.
Izumi's backstory in the manga where we find out that he killed himself when he was six standing in a railroad crossing, because he felt that his mother didn't want him. It turns out that his mother let him go because she felt like she wasn't able to love him.
The ending of the manga, with Mitsuki's song.
Takuto singing. It's so painful to know that he could do that forever and nobody would ever hear him.