Izumi gives him a knife.
Anyone else would be confused to receive something of the sort from their daughter, but not him. To him that knife holds more meaning than if she gave him all the secrets of the universe.
He remembers when he would find multiple of those just lying around his room, occasionally scratching his hands or arms because they were always under a blanket or a pillow. How she always fiddled with one whenever she was bored, swirling it around around her fingers, carving shapes in the floor or on the trees, once even trying to teach him to aim and throw it perfectly, but then giving up as it annoyed her even more than an orange sunset.
He wasn't around when she became well-versed with her weapons, but even with the old image he has of her in his mind - a shy girl with pink ribbons -, for him those knives would always be a part of Mai.
Now, after a wave of nostalgia, he holds the knife in his hands. The shiny and sharp ones from his memories replaced by the opaque and dull one on his hands. The rust and signs of abandonment only making the melancholy grow stronger on him.
"The kids found it while playing in the garden," Izumi explains with a soft voice, "I think she lost it during practice and never noticed it."
Zuko nods slowly. That would make more sense as there was no one else carrying those knives around the palace, "She always left these on the most inconvenient places."
He wraps his hand around it, a wistful smile holding back any tears that he might still have. Unlike all of the others, this one he won't give away, nor will he put in a glass to be exposed to the next generations.
This one, old and rusted like he is, he will take with him. He will carry this small part of her, even though it does not serve to anything anymore.
He'll have a small piece of her with him until he is finally able to join her.