Marina Koizumi is a classmate and friend of the Ojamajos. After the first two seasons, she is in class with Aiko, Onpu, and Hazuki.
Marina is a very kind girl often seen the background and has spoken many lines earlier in the series.
Currently, Marina is in a relationship with Kimura Takao, who struggled with his own feelings for her. Both as a friend and maybe something more, but each time they have worked it out and managed to develope a relationship.
Marina is voiced by Ichimura Oma.
Soft spoken and maybe a little shy, Marina does a lot of kind and caring things for others. This is most seen around school, such as bringing fresh flowers to class, cleaning, and wiping the desk in the early morning hours before class begins. A lot of people seem to like her, but due to this she has been called a Teacher's Pet. This hurt her feelings and left her in severe shock.
She really loves flowers and gets angry or upset if someone injures or harms them without caring about the consequences. She is in the school's Garden club and even takes care of the flower garden behind the school. At first, Marina reveals that her mother had convinced her to take care of the flowers and encouraged her to do this as Marina felt that she wasn't good at anything or even that smart. But now she really does love flowers and wishes to take good care of them.
Marina is closest to Hazuki in the Ojamajo group, and she may also be friends with Sachiko ljuuin, who she has been shown with on multiple TCG cards.