Note: she is not really in Kodomo no Omocha. She is the character of the movie in the show. Mako was the girlfriend of Hiroto Suzuhara's eldest brother, Masato Suzuhara and friend of Miwa Nakagawa. She, along with Masato and Miwa, went missing for 6 years. When Hiroto decided to search for his lost brother in the villa that Masato was supposed to have go, and that it was supposedly not found, he met with Mako. Mako lead him to his brother only to find out that both him and Miwa had grew up but not her.
It was later found that she was a ghost that had been haunted both Miwa and Hiroto since their vacation to the villa. As said by Mako, she is like an incarnation of hatred and sadness and it seems to have ghostly powers in the form of water. Eventually, she likes to torture psychologically Miwa and Masato as she is show how she tortures Masato when giving him the herbs. Mako slowly starts to fall in love with Hiroto since she sees that he has a kind heart and at the end, she let him go.