What is the title of the song played around this part? I really wanted to know the title of the piano piece or at least the composer. I tried searching for Pupa OSTs but unfortunately only the OP and ED were released.
Pupa's OST was composed by KONISHI Kayo and KONDO Yukio (who, together, make up the musical unit MOKA☆). Unfortunately, I think that's as good an answer as you're going to get, given that the soundtrack hasn't been (and, I'm guessing, never will be) released.
If you liked the music in Pupa, perhaps you would like to listen to the soundtrack of Elfen Lied, which was also composed by Konishi and Kondo.