He despises her.
Maokai has stood on the fields of justice for far longer than any other champion, longer than the fields have officially been there themselves. He knows, though he can't understand how, the cycle of life that had been in place before the putrid humans ever showed their face. Back when it was simply the animals and plants, the world was pure. There was no evil, because evil could not exist in a lack of sentient. But when man came, bringing with him his tools and his weapons and his magic, everything changed. The land had been torn apart by industry and war, the balance of magic disrupted to the point of no return. And he hated them for it.
But her he despises more than any other. The very thought that she would give up her heritage, her true lineage as a plant, and embrace the body of a human made him quake to the core with disgust. Zyra's plant form was twisted to sentience, similarly to his; the magic of the Rune Wars did terrible things to the earth. But when she chose, freely, to accept and take the body of a mortal, she made the ultimate betrayal to her kind.
Maokai had seen many things from the time he was a sapling to when he joined the League. He had witnessed most of what the humans had to offer, and knew that nothing good could ever come of it. He cared not for the power that sentience brought, nor the ability to reason. By logic's standards, it was the mortals themselves that gave him the ability to hate them. And he would abuse that ability to the end.
When he first saw her, Maokai had almost felt something close to relief. He had assumed that her story was similar to his; brought to consciousness against her will, looking for a change back. But it wasn't long before he realized that not only had she chosen this fate for herself, she also never intended to return. He mocked her lust for power, greater than many humans by now. She was an abomination, a disgrace, and sacrilege to everything he knew to be true and pure.
Maokai hates all humans, any sentient being. His anger fuels his fights, and he will not rest until he changes back or they are dead. But Zyra holds a special place of abhorrence in his mind.
He despises her.
She pities him.
Even with her human memories, Zyra is driven with the same instinct she's had since her creation. She preys on the weak, growing stronger as she devours any who are careless enough to fall into her trap. Man, woman, child; it doesn't matter to her. She cares not for their personal struggles or problems. She is a force of nature.
And yet, she pities him. She sees the power he possesses, the strength which runs through his roots and branches. In her hybrid mind, the natural lust for power and the human concept of emotion merge to create a strange attraction to him. She doesn't understand it, nor does she really care. She can always sense where he is outside the Fields of justice, feeling his body move with her mind. He is always able to tell, and is constantly blocking her out. She sometimes wishes he would join her in power, to overrun the living in an army of vegetation. But his old beliefs keep him rooted strongly to the ground, and for that, she pities him.
His opinions of her are no secret; when she had loudly proclaimed that she had no intention of going back to her old life, he nearly crushed her. His bellows of rage shocked those standing around, even as the summoners held him back. She could feel his power coursing through his roots and branches, the air crackling with the magic he possessed. For her, it was euphoric.
He will never be able to break his single-tract mentality, she knows. His only goal is to revert the world to what it was before. But she knows the truth; there is no going back. The humans had changed things, permanently. To wish for the old was useless; to embrace the new was wise. One must discard the notions of peace and balance, finding instead true power in a world of rising titans. She will obtain this power, and a small part of her wishes he could see it and join her. But he never will.
She pities him.