Little is known about Machi. Her parents are fishermen and she has described her older brother as being similar to Ushiro in behavior. She was the one who discovered Kokopelli's cave and she was reluctant to sign the contract but Waku's push forced her to become a part of it. When the children were introduced to their chairs, Maki initially thought Machi's chair was hers.
During Chizu's scenario, it was Machi who chastised her about her senseless killing of innocent civilians. During Kanji's story arc, Kanji warns Jun to "watch out for Machi", and later, when he sits atop Chutenro Tower waiting to die, he contemplates who the next pilot is, but for some reason, rules out Machi, implying that there is something that he knew about Machi but did not reveal to the others. She later reveals that she's Dung Beetle's Sister and she wasn't part of the contract because she was from another earth but later she decides to sign again after Ushiro, revealing that being of another earth was not the reason for being out of the contract.
In the anime series, Kirie not only deduces that she is the one not bound to the contract besides Kana, but also that she knew more than she let on, as she was the one who attracted the rest of the children to the cave where they made the contract and also knew better about the rules than anybody else. Koemushi reveals that she is in fact, his little sister, sent with Kokopelli to the children's Earth with the mission to gather the rest of the pilots. Machi can also telepathically talk to Koemushi. Tired of seeing the same story of suffering and death being repeated at each world she passes, Machi ends killing Koemushi and helping Jun to protect her sister by assuming Misumi's place and becoming one of the pilots, instead of Kana, like he had planned.