Relating to the karma seals of course. I think its a characteristic of their karma seals being linked that allows their power to grow exponentially. So what I think is gonna happen is they are gonna get really strong really fast. I think this is caused by the relationship between Ishiki and Momoshiki. They may be the same person like two halves of one whole. You know how the Otsutsuki can eat each other? What if it works the opposite way also? This would make Boruto and Kawaki's karma seals be linked to the same individual but different versions of him or her. The effect of them being in close proximity makes them more powerful because of this.