Menma has black, messy hair, from which one lock of hair is always standing upwards. He's height is average for his age and he has gray colored eyes. He wears a black t-shirt with the Hidden Shadows band on his arm. To accompany this, he wears black bottoms and black shoes that cover his toes. He also wears jet back finger less gloves.
Menma is a carefree lad who cares deeply for his friends. He is a bit of a trouble maker and thinks everything that doesn't amuse him is lame. Menma is quite aware of his physical capabilities and underestimates every single one of his opponents. This ofter gets him into trouble.
Birth name Maruta, Menma was originally conceived by his mother Sorae in order for her to continue her research with human testing. Shortly, after his birth his presence awakens the maternal instincts within his mother. Hagire meets with Sorae in the maternity ward and rejoices at the thought of continuing his expirements and goes off to prepare. Soon afterward, Sorae had begun regret her choice of using her child as a subject for her experiments. After a conversation with her lab assistant and presumably Menma's biological father who offers to take the child and leave, Sorae procures another child to be used as a test subject in his place, Shiro.
When he was little, Menma lived with his mother at the research institute where Shiro was being experimented on. He met the girl and told her he liked her hair and became her friend and playmate.
However, he did not know the torture his mother and Hagire Rinichirō put her through so he did not understand when she lashed out at him in pain and broke his Aceman doll, causing him to reject her. However, she saved him from a rabid dog and their friendship became stronger.
Another time, Shiro accidentally hurt him with her strength when they were playing, but he impressed her when he stood back up.