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 pushing her hand onto the sensor forced her to become a part of it. 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. At the start of Kana's story arc, Machi is finally revealed to be related to Coemushi.
In the manga, at the time when the children are introduced to the chairs, Yoko is not conscripted, and therefore, like Jun (who himself takes Kana's chair), has no chair of her own. The one she claims is Maki's, Maki having mistakenly thought the baby cot (intended for Chizu's baby) was her designated seat.
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. Coemushi 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 Coemushi. Tired of seeing the same story of suffering and death being repeated at each world she passes, Machi ends up killing Coemushi and helping Jun to protect his sister by assuming Misumi's place and becoming one of the pilots, instead of Kana, like he had planned.