You two have been together for the longest time, even before he became the thing he is now you two have been together, it has always been Nier, Yonah and you and Nier has always fought to keep it like that, no matter what form he takes or what he becomes everything he has done has been to keep his family together
From the start he decided to participate in this cazy plan just because of the promise to be able to be with you two again, he became the Shadowlord because that way he could concrete the plan himself and leave you two have new lifes, so he would be able to have his family together, after gaining the title of Shadowlord and enough freedom he spend quite some time searching for you two, first the shadows, the souls, he kept yours and Yonah's shadow inside of his castle, somewhere safe from sunlight and where he could protect you two, then the replicant, the new bodies
But the plan failed and the replicants gained counciousness and lifes, they saw themselfs as the humans and the shadows as monster threatening their lifes, despite following their exact original life
Nier's and your replicant met each other and, like with the originals, you two have grown to be close to each other, the three of you became to be like family, you were there to help Nier in whatever you could, you were there to take care of Yonah when Nier was too busy, you were there to share meals and laughs, to share the bad moments and worry, you have become important part of their lifes and Nier knew that he would do everything to protect you two and this life, just like the original had thought
At the end, that obsesive love and fierce wish to protect was the same, was shared, born from the same heart and for the same person, in both it has been triggered by their counterpart, the Shadowlord was enraged that his replicant dared to have the life he has fought to have all this years, that he was so free when the three of you had to hide inside of his castle, that the future and freedom he has been promised so long ago it was taken away from his grasp when he was so close, but that is why he decided that he will snatch it from that replicant before he could do anything, that was how the Shadowlord aimed to kidnapt Yonah and you from Nier's side
And, in consecuence, Nier's obsesive love over you was also triggered because this monster was trying to take away his family, he fought with everything he had but this has done nothing but start a endless battle, even if Nier managed to same you the first time he would not be enough to protect both, you and Yonah, but since the Shadowlord wasn't going to let go of this easily Nier was ended up forced to become more and more protective over you. He would never dare to hurt you but was too scared of losing you, he was even willing to beg you to please not leave his side, not even his sight, for whatever reason that shadow seem to want you specifically and he is too scared of losing you, he will grow stronger, faster, he will become your shield but please never leave his side
At the end this is nothing but an endless fight, non of them will rest until they manage to win this fight and be able to have you, both love you too much and both will do anything and everything to have you, to be a family again, so this will only end until one of them comes out victorious
