One common theme is the struggle between duty and love. Goemon as a ninja likely has certain duties, and his love interest might conflict with that. Another could be the secrecy of the relationship, as ninjas often operate in the shadows.
In 'goemon ninja love fanfiction', a prevalent theme is the clash of two different worlds. Goemon's ninja world which is full of danger, secrecy, and discipline, and the world of love which is more about emotions and vulnerability. This contrast can lead to many interesting plot developments. Another common theme is the discovery of self - through love. As Goemon falls in love, he may start to question his identity as a ninja and his place in the world. This self - exploration adds depth to the characters and the story as a whole.