Tomoo is a young orphan boy who appears in the eighth episode of Elfen Lied, "The Beginning". Although he only plays a minor role in the series, he is also its most despised character, for reasons described below. He is voiced by Reiko Takagi in the Japanese version and Chris Patton in the English dub.

Tomoo was a student and resident at the orphanage where Lucy grew up. He and his friends regularly tormented Lucy because of her horns, but Lucy always avoided displaying her emotions which only encouraged Tomoo to torture her further. After Tomoo and his friends found out that Lucy had been secretly taking care of a stray puppy, Tomoo proved to Lucy just how malevolent he could be by taking a vase and beating the puppy to death while his friends made her watch. This meaningless act of brutality is what drove Lucy to use her vectors for the first time and she butchered Tomoo and his friends.

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