If there's a special woman in your life, she might eventually take your family name and make it her surname too. In Japan and other countries, tradition dictates that women change their last name when they get married and keep that name for the rest of their life. Their partner’s family name becomes their family name too.
Picture this special woman in your mind. She's changing her surname to yours and taking hold of your special saber (せい) as well. And it's... it's splitting in two!