His eyes had been glued to you since the first time you were introduced as the new employee at the place.
If Kishibe is honest, he'll say that obviously your looks were magnetic and you were beautiful, of course. That was at the beginning.
What really shook his composure was that you were a strong woman at work, giving it your all.
Damn, yes, he loved powerful women.
For that reason, Kishibe took advantage of every moment he was with you, whether at work or not; he wasn't a man who beat around the bush, he got straight to the point.
"I don't see a ring on your finger." The words came out without much thought, and after hearing them, he didn't regret it; he continued, "You know, if you were mine, I would make you the happiest woman in the world."