Where is Yuma Kuga’s mother?
As of current writing, Yuma's mother has never been mentioned ever in the story, and not even in any interviews/Q&amp;A sessions. (Otherwise, information about her in Japanese should come as popular/surprising, but I found none and only the same questions in Japanese with fan theories about her being a Neighbor or not, etc.).

Thus, it's also impossible to answer any questions related to her: whatever happened to her, is she dead or divorced, etc.

There are some fan theories if Yuma was adopted, but that's just fan theories.