Mayumi is Ota's mother. Over 30 years ago, she and her husband took out significant loans to open Matsushita Diner near the Kabasaki District. She has been running the diner ever since. Lately, her memory has begun to get spotty.
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At some point in her life, Mayumi became ill with alzheimer's disease specifically resulting in progressing dementia.
In the Ota Route, Kaname Date enters her somnium; PSYNCIN' IN THE SUSTaiN. This somnium allowed the player to experience her important memories. Her dementia caused her to forget Ota Matsushita's involvement in the attempted murder of both Iris Sagan and Ota Matsushita in the Okiura Fishery Cold Storage Warehouse. She later is able to remember the events that transpired, revealing that she had called a taxi to follow after Saito Sejima (In the body of Iris Sagan) and Ota Matsushita. This lead her to believe that Ota Matsushita was the culprit behind the attempted murder, which caused her to attempt to feign guilt to protect him.
|AI: The Somnium Files|
|Day 1: sigAI||Day 2: saikAI||Day 2: meikAI||Day 3: syokubAI||Day 3: rihAI|
|Day 4: youdAI||Day 4: jikAI||Day 5: zugAI||Day 5: syokuzAI||Day 4: syougAI|
|Day 5: seisAI||Day 6: hiAI||Day 6: sanpAI||Day 3: gumAI||Day 4: jukkAI|
|Day 4: kikAI||Day 5: jinnAI||Day 5: ihAI||Day 2: keitAI||Day 3: gyoukAI|
|Day 3: kyuusAI||Day 4: syuurAI||Day 4: irAI||Day 5: dakkAI||Day 6: kekkAI|
|Day 5: kenzAI||Day 5: jutAI||Day 5: kokkAI||Day 6: sousAI||Day 6: hakAI|
|MaiN: 1||MaiN: 2||MOUNTaiN||CHaiN|
- In a fan-made Character Poll for AI: The Somnium Files held on Twitter, Mayumi Matsushita came in 11th place.