I had a set of ideas related to the Gen 8 Legends based on someone's old suggestion. It was something where you'd need help from Zacian and Zamazenta to beat Eternatus before having the MC Dynamax his dick to fuck her.
My idea is that it would be fun if you had to fight Eternatus before catching the wolves. This would match the order of events in Sword and Shield, and give Zacian and Zamazenta funny potential since they would see the insane sight of you fucking Eternatus before you get them in the harem.
From there, my specific idea is that one of the two wants to get the same Dynamaxed pleasure from the MC. It would be a reference to the post-game where they get hit with Galar Particles by Sordward and Shielbert. The difference would be that Zacian or Zamazenta would want it to happen to them. Just like in the originals they aren't able to Dynamax and the particles would just enrage them... possibly since they can't have colossal dick like the cannon dragon. Then it'd be a normal fight and breeding scene.