The hilt guards did have all levels of meaning during the Edo period. The warrior class generally being forbidden to wear jewelry of any sort, the guards became a favorite place for circumventing the rules. It can be quite the undercurrent of the art and philosophy of that near 300 year period. I must confess that I don't know much about the Christian ones. There was a very authoritative article published on them by a collector out in Nevada or Arizona, I believe by Mr. Geyer.
The Japanese owner of this one published it as 'Geranium', which I could not see. This morning my wife provided me with this image of African geranium. Ironically, the owner works in or with an African Art Museum. He may be seeing what is closest to his own daily art dive.
I don't know what prompted me to look into it more than curiosity. The rendering is more folksy Korean than Japanese, but then the Japanese had just invaded Korea at least twice and were bringing back much in the way of tea bowls, food, cooks, art, etc.. I enjoyed an article by Zoë Templeton on the Cultivation and Culture of Wasabi and been struck by this second attached image. I lean towards thinking of it as wasabi formerly known as wild ginger. As a foreign exchange student long ago, I had fresh grated wasabi given to me at the dinner table. My tolerance for spice is much higher now than then, but that was still a unique kick to the head. It was nothing like the horseradish paste we call wasabi on USA sushi. I've very rarely had it since.
I lean towards it being Wasabi, but am still relatively new to learning in this area. My ability to distinguish is still very crude at this point.
I welcome anyone that might provide further insight.