The lengths the duo must go to in order to get the most optimal timeline is shown right from the second episode, where Matsumoto stops Diva from saving Momoka, the girl who always believed in her and gave her the name Vivy.
The discovery that all of the vicious rumours spread about Estella, before and after her supposedly causing the Colony Drop were false, as she was framed by her twin AI Elizabeth and Toak. The worst malfunctioning AI in history as per the original timeline really was just a kind Sister unit who wanted nothing more than to make people happy.
What happens to Grace and Dr. Saeki in the new timeline. it turns out that Dr. Saeki and Grace were never married in the new timeline, as Grace was assimilated into Metal Float before Saeki could propose to her. He had hoped the shutdown virus would allow him to retrieve Grace, only for it to backfire as the virus affected Grace's programming and cause the A.I.s to go berserk. Concluding that there is no way to save Grace, Vivy and Matsumoto entered the core and destroyed Grace to shut down the rampaging A.I.s before they could do more harm. This caused Saeki, now grieving over the loss of the love of his life, to kill himself in the church where he would have married Grace, sending Vivy into a Heroic BSoD as her actions compromised her mission to make everyone happy.
The Death of Personality Vivy suffers after the malware wipes out the Diva personality, as well as her ability to sing. Seeing Vivy reduced to being in an AI Museum is quite sad.
