Very interesting... I'm wondering if Duke Castillo actually did also reincarnate. It's the only way that his interactions make sense. The handkerchief was on purpose, he heard Lippe's singing, he used the same non-pickup line, and he has an abnormal interest in her despite usually being uncaring towards anyone else. And by now, he's probably observed enough of Lippe to understand that she likely reincarnated too.
This will be interesting to see how this develops...