When Joyd was reborn into a new host ten years ago, he was rather full of himself and decided that just one host wasn't enough, he wanted more. And so he split, half of his powers going to the Noah we know as Tyki Mikk.
Tyki Mikk awoke when he was sixteen and went to the Family, balancing both his white and black life like normal. Only Rhode knew that there was something off about Tyki, and it wasn't him suppressing the Memory, though he was doing that as well.
The other half of Joyd went to a nine year old at that time, a redheaded one currently learning to become a Bookman. Bookman told him the headaches were just a part of the training and perhaps over-training. But because of the training Joyd could not exert any kind of control or influence on the young mind like he did Tyki.
The Memory finally got his chance when Bookman and the newly named Lavi reached the Black Order. Tettsui would not accept Lavi at first because of the Noah's presence - even with Joyd asleep - but the Innocence reluctantly accepted the redhead as its conformer. And with the trying new record for being the first time on the front lines and in the war itself, Joyd had a way in and exerted his influence on Lavi's relationships. It pleased him to make them, make them strong and binding to cause his host discomfort and confusion.
Everything continued like normal in canon until Japan when Tyki and Lavi briefly fought. There was a moment of recognition between the Noah and the lurking Memory within the Bookman apprentice but Tyki forced himself not to say or do anything about it. As he was there was no way to really talk to Joyd within his head, he had no knowledge of Joyd.
Rhode recognized fully what had happened during their little game in the Dream, getting pissed at him and practically tearing into Bookman Junior with more fervor. She didn't include just those that he had recently formed bonds with but those that he might have had a connection to in the past as well, Doug and those from records past. The Memory was pissed that she was toying with his host in that way and actually helped Lavi figure out how to defeat her there.
However, Lavi's fight with Allen while being without a heart shocks the Memory into waking as soon as Allen's sword impales him. His training allowed him to keep control long enough to finish the canon fighting though his reactions were definitely slowed. During the time of brief death in the Ark helped silence the Memory longer still but the damage was done and Lavi knew that there was something within his mind that wasn't normal. He doesn't get a chance to really do anything about it as canon events continue as normal, the Memory biding his time.
That is until Bookman and Lavi head to China but before the Noah appears before them Joyd grabs control and yanks his host away from Bookman.