Originally got this info from a tutorial by SilverWuffamute Plays which can be found here: • VRChat MMD Viseme/Shapekey Tutorial - Upda...
Japanese/Phonetic/VRC Viseme
あ = "ah" = aa
い = "ee" = ih
う = "oo" = ou
え = "eh" = e
お = "oh" = oh
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