For Odd, definitely Mauve. Mauve's can be haughty/overly critical in the present, but it was even worse when she and Odd first met and their lives got tangled with each other. Though while she started off a little prickly and suspicious of him as a boy, she eventually softened on Odd after he kept trying to be hospitable through her grumpiness, and began to legitimately trust him after he helped her through some episodes of her getting blindsided by her dormant powers from her time as Seidallah, at a time when she didn't know about that aspect of herself.

(And I would've said Giratina, but neither Odd nor Gira themselves consider their relationship of the standard trainer/Pokemon dynamic. And even if they did, the process between them would be more akin the them training each other so they could both exist in relative harmony without hurting each other.)