She suffered a head trauma that caused cerebral stroke, inducing aphasia which resulted from a blow when she try to stop a fight between her parents and her father hit her head with a glass beer bottle. However just when she was just getting into the business she became ill and fainted at a part time job that she was working at. On one getaway from their fight, she began listening to a band called Sad Machine and stumbled into the world of music and began her music career. It is revealed that her parents often fought during her childhood. Her citizenships are Japanese from 1996 to present, and American from 2013 to present. She is often seen as stubborn (as Angel whom she mentioned to be very persistant) at the beginning but as she got to know Hisako better, Iwasawa was actually a clueless, innocent bad-in-naming-the-band girl. In the manga, Iwasawa can be seen to have a rather comical attitude towards her band mate, Hisako, which often result in Hisako getting angry over Iwasawa. This eventually changed when she meets Yuri, who aside from Hisako has been the first person to show sincerity towards her. Masami later reveals that she feels uncomfortable when interacting with other people as she experienced being gossiped behind her back when she was still living, and has once showed a facade to people to actually talk to her, hiding her true feelings inside. Even so, her usual conversations with the group are composed of plans for a new song for their next performance. She is very focused to making music to the point that only the fellow members of Girls Dead Monster are the only ones who are able to talk to her she is usually described as a 'music nut' by her bandmates. While usually she is rather quiet, she is able to fascinate listeners by striving to create music that speaks her thoughts and feelings. She wears a helmet typical to Yukari Morita's space helmet, appearing in episodes 22, 26, 28, 29, 32, and 33 of season 3. She wears normal school shoes as well as black sweatbands on her wrists.

Iwasawa has chin-length pink-red hair with two locks of hair longer than the rest, extending to her back.

Crows zero final battle song