Well, it could make his combat style more versatile. He might be able to analyze his opponents' moves more precisely. With six eyes, he could have a wider field of vision, detecting attacks from more angles. Maybe he can use this new visual ability to anticipate his enemies' actions better and counter them with more effective jutsu combinations.
Gojo's power of the Six Eyes could help him detect magic in ways the Fairy Tail wizards can't. For example, he could see the flow of magic energy in a battle and predict his opponents' moves better.
The story dynamics would change a great deal. Firstly, the mystery around the Six Eyes would draw in different characters. Some might be curious, some might be envious. This would create new relationships and rivalries. In addition, the training and development of the Six Eyes power would be a central focus. This could lead to different story arcs as the character with the power tries to master it, and other characters either help or hinder this process.
Marin does confess to Gojo in the manga. It happens during a crucial moment when their relationship reaches a turning point. The confession is filled with honesty and vulnerability.