Menstrualine is the final episode of the first season of Pubertina.
The kids at school were laughing at a girl who is crying, who appeared to have acne all over her face and small nubs where her breasts should be. Deb runs over to Pubertina at a table, telling her about this girl and point out that she's just like Pubertina. Acting heroic, Pubertina demands Deb to take her to the girl.
Pubertina and Deb find the girl crying and poking at her breasts. Pubertina admits she never done anything heroic before introducing herself to the girl, who introduces herself as Menstrualine. Deb thought it sounded French, but Menstrualine says that it's just ugly. Pubertina tells Menstrualine, who she nicknames Mensie, that Pubertina herself has been going through it for six months and it's happened to all the females in her family for generations. Pubertina tells Menstrualine that she has coping techniques on how to cope with puberty in the form of a song.
After the song, Menstrualine starts to ask a boy to the movies, to no avail since the boy just walked out. Deb compliments on Menstrualine's newfound confidence. She also says that she probably needed Pubertina when she's going through puberty, but Pubertina points out that Deb isn't going through puberty yet. At first, Deb is annoyed for pointing that out, but she suddenly sees a breast nub pop out of her chest. Post credits, Deb starts to freak out and asks if it's all a dream.