Episode 4: Eu confesses the truth about her powers, convinced Ayumu will hate her for being a monster. Ayumu won't have any of it, and swears to stay by her side no matter what comes their way.
Episode 11: Eu speaks after Ayumu told her not to leave again. Not write, SPEAK. Not just one sentence, about 5-6!
Episode 12: Ayumu takes Eu's powers temporarily, with the help of a machine Doi-sensei just happens to have brought along, to allow her to join in with all the other girls singing. Then when the machine's batteries run out Eu stops singing until Haruna tells Eu to hold her hand so she can use her powers to help Eu keep going.
1st OVA: The reason for Taeko's crush on Ayumu is revealed: when they were children, they helped take care of a stray dog together.