The first thing to cross his mind when he saw her was that she looked different.
He wasn't talking about her hair or her outfit because those were insignificant details that were bound to change. Nico Robin looked different. She looked softer as if she had finally let go of the pain of her past. She was more approachable now than she had been two years ago even if Zoro could sense that she was much stronger.
He hated to admit it but this worried him. There was a small, demeaning part of him that needled at his conscious, telling him that now that Robin was healed in a sense she wouldn't want to be with someone as damaged as him. The physical scars were never an issue and she wasn't vain enough to care about his eye but two years under the tutelage of Mihawk did nothing to silence the ghosts of his past. He might be closer to achieving his dream but he could never forget that Kuina never would. He was as determined as ever but some ghosts you just couldn't let go.
So he didn't want to admit it but he was scared.
He should've know better of course.
It wasn't until later when they had all rejoined on the Thousand Sunny and began their journey downwards that they were afforded their first moment of privacy. There was no tearful reunion or grand exclamations of love; that was never their style. Robin simply walked into the room they had shared many a night in and gave him a kiss. Their lips touched and despite all the changes and time the spark was still there. The desire for more, always more singed through them and when they pulled apart Robin was smiling her secret smile.
With that one simple word Zoro realised he had absolutely nothing to worry about.