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Reminder that even the most believable yuri relationship is a lie between vtubers.
They will call each other "wife" all the time because that has no basis in realty but a Japanese person is not going to say in a completely serious tone, "She is my girlfriend and has been for x months/x years." That would feel too real, too embarrassing to say even as a joke and they would likely never bring up their relationship on stream if it existed for real.
They make yuri a show for the audience because it never truly intrudes on their private lives.