Sword Art Online: Alicization

A flashback occurs to when the Administrator is losing her own memory space, and so gets a child to link their memory. But this was a fatal mistake of the Administrator, because this means the child gets the same authority and power. This comes to the attention of the child (which is now to be revealed as the cardinal of the great library) and so, she attacks the Administrator. She flees to the one out of two places the Administrator doesn't have authority over, the great library. She spends the last 200 years thinking of a way to defeat the Administrator and finds Kirito and Eugeo in the process. She also explains how to get the Integrity Knight's memory back. Thus, the Cardinal allies with Kirito and Eugeo to defeat the administrator and get back Alice.