In the manga, Tanjiro and Kanao don't end up getting married. The story focuses more on their battles and character development rather than romantic pairings.
I'm not entirely sure specifically what 'x change r visual novel' is about as it could be a relatively unknown or niche title. It might involve a story with characters whose relationships or situations change (the 'x change' part) and be presented in the visual novel format which typically has a combination of text, images, and sometimes audio to tell a story.
I'm not sure where you can specifically find 'x change r visual novel'. It could be on some niche visual novel platforms, or if it's an indie creation, perhaps on the developer's own website. You might also try searching on popular digital game stores, but it really depends on how widely distributed it is.