An idea for Solgaleo, Lunala could be since they are both in the same region them just being their causes a solar eclipse to happen but wont go away till both have been dealt with since both are against the other and would fit. With Necrozma can be in a area that is shrouded in twilight and cant be entered till both other legends join the MC. The best way I can describe the twilight would be darkness bleeding from light or to look up "legend of Zelda twilight princess" twilight zone, where like Necrozma got their light stolen and would look good as the background of the images for her. Since the MC had sex with both Solgaleo and Lunala his dito genes now have him make the same energy that Necrozma needs to have to stop feeling pain she is always in and is made and delivered by his dick so once she tastes him she will want to stay with him since he can make an excessive amount at any time.
I also had an idea for any of the futuristic paradox pokemon that could be used that can say why they are a paradox since there is little info on them from the future on them. It goes like the MC breeds the robotic paradox pokemon (not joining harem) it is then speculated by Maple that the one that was brought back from the future is a future descendant of his where its been so many generations without the MC where incest would not be applied that was randomly chosen to go back and start a loop that would have no beginning or end thus a paradox.