ok so get this: AU where Jötuns lay eggs
Now consider: Loki, of course unaware he's a Jötun, loses his virginity with Fandral. Things go well at first, until Loki nears his orgasm. He gives a final thrust inside Fandral, and it all goes wrong from there.
A knot forms at the base of his cock, trapping the two of them together. Fandral panics, and think this is some scheme Loki has planned with his magic, but it becomes clear that Loki is just as confused and worried as he is.
Soon, the first of the eggs make their way down the length of Loki's cock, before they are pushed out, settling inside Fandral. The process isn't painful, though it is alarmingly pleasurable for both of them, leaving then almost resigned to what is happening, all thoughts of what will happen next morning forgotten as Loki fills Fandral with a clutch of his eggs 💕