Gray noticed it after almost a year and a half after she joined Fairy Tail that his ice felt different when he had Juvia's water as base.

It was somehow a stronger type of ice; even stronger than making it with both hands, like Ur taught him. He never thought anything of it, but he was sure now: his ice was different; thicker, stronger, more consistent. It made sense, though: instead of creating it out of 'thin air', he had something to base on.

Maybe only one other person in the world could see the difference between his magic's consistencies. He was sure that it was why Lyon said something about him 'defiling' Juvia's water. It was funny, though; it didn't seem like he was defiling anything.

It felt like her Water was made to make his Ice stronger.

Gray remembered how much stronger he got when they were fighting Lyon and Chelia, even before the Unison Raid, the attacks that originate from hers, were stronger.

He made a mental note to stay close to her when the dragons arrived. He might need the extra strength.

Looking over his shoulder to where the Water Mage was with the small pink haired girl, he saw Juvia giggled at something Chelia said and it surprised him that even in the situation they were about to face, she would still smile. Juvia caught him looking and offered him a smile.

Yes, he was going to stay close to her, so both of them could get stronger. Because, somehow, that was what they were meant to be.