How do you think it was the love story between Undertaker and Ciel's grandmother?
Well, if there was love between Claudia and Undertaker I think they rather kept it in secret. Undertaker and Claudia may have met during a case Claudia was on as the Queen’s Watchdog. Undertaker may have been involved in that case or he may have offered his assistance if he already worked as a mortician back then. They may have worked together and then fallen in love with each other. Maybe Claudia even knew that Undertaker was a shinigami.
However, because of Claudia’s position (and depending on whether Undertaker is Cedric or not there may have been another man in Claudia’s life) I think that their love was a secret. No one really knows anything about Undertaker and even though Ciel knew that his father knew him, too, he didn’t know there was a connection to his grandmother (maybe not even Vincent knew). So Claudia and Undertaker may have met each other secretly.
I’m sure when Claudia died Undertaker was devastated. I suspect that Claudia was killed (similar to how Vincent died) and Undertaker probably blamed himself for not being able to protect her. That’s why I think he made a promise to keep an eye on her children and successors and that’s why he always seems to be around the Phantomhives ever since.
