Regardelss of the Bahamut inside, the crystal has its own limited awarness. It knows it's there to help the Lucis line. But then Regis dies, and the only Lucis Caelum left alive is Noctis and he's in constant danger. Well, the crystal can't have it - the Royal Line must continue!
So it influences Noctis so that he feels the need to impregnate someone as soon as possible... And isn't it great that he travels with a fertile woman, fem!Prompto, to whom the crystal also has access through Noct's magic? A few mental shoves in right direction and she is also absolutely happy to be bred by the Prince. Cue Prompto and Noctis having sex every few hours, regardelss if they are in public or not, and seeing absolutely nothing wrong with it.
Bonus points if it lasts awhile and Ignis and Gladio (and Cor) try their best to make sense of it all and somehow control the situation - and fail miserably.
All the cookies if Prompto and Noctis are completely normal and rational in every other aspect, but then they're like "Just a minute Iggy, Noct's gonna fill me to the brim with his cum and then I'm gonna help you with the dishes" or "Well, that was an intense fight... Gladio, could you get down from that rock, I'm going to fuck Prompto full of babies there."
Noctis/fem!Prompto, dub-con, impregantion, Crystal made them do it
So it influences Noctis so that he feels the need to impregnate someone as soon as possible... And isn't it great that he travels with a fertile woman, fem!Prompto, to whom the crystal also has access through Noct's magic? A few mental shoves in right direction and she is also absolutely happy to be bred by the Prince. Cue Prompto and Noctis having sex every few hours, regardelss if they are in public or not, and seeing absolutely nothing wrong with it.
Bonus points if it lasts awhile and Ignis and Gladio (and Cor) try their best to make sense of it all and somehow control the situation - and fail miserably.
All the cookies if Prompto and Noctis are completely normal and rational in every other aspect, but then they're like "Just a minute Iggy, Noct's gonna fill me to the brim with his cum and then I'm gonna help you with the dishes" or "Well, that was an intense fight... Gladio, could you get down from that rock, I'm going to fuck Prompto full of babies there."