Had an idea for Gen 7 that's kind of a fusion of other ideas. The first of those is how the MC fucking Necrozma would relieve some of her pain due to connection to Solgaleo and Lunala. The other idea was how the MC would go to a genderbent dimension for one of the Gen 7 box Legends, since the two are opposite genders according to the original pokedexes.
My suggestion is that the MC is able to relieve Necrozma of pain by using either a Solgaleo or Lunala dick while fucking her. This would give a use to the MC encountering the male legend, it works with Necrozma's lore since we can say she's getting "light" when he fucks/cums in her, and it would give us a rare opportunity to have the Legendary Pokemon take a Legendary Dick.