Miyamoto is the mother of Jessie, and a former member of Team Rocket. She disappeared while on a mission to capture a Mew for Madame Boss and hasn't been heard from since. Miyamoto was an active-duty Class A Rocket. She was the first person to get tangible evidence of Mew, a recording that she took in the South American jungle. After filtering out all background audio, she was left with the faint cry of Mew.

When she showed this recording to Madame Boss, she was sent on a mission to capture Mew. Miyamoto was torn over having to leave Jessie behind, as she was still a child at the time, and thus she carried a photo of Jessie at all times. While on her search through the Andes Mountains, Miyamoto got lost in a blizzard. The harsh weather suddenly broke, upon which Mew appeared before her. After she showed Mew a picture of Jessie, she tried to convince Mew to let her capture it, but Mew vanished and the blizzard returned. An avalanche started and Miyamoto's scream was the last thing that was heard. Ever since, she was presumed dead.

However, she still made reports in the subsequent years, and Giovanni stated that her current whereabouts are unknown. As far as it is known, Miyamoto may still be looking for Mew.