This is actually fucked up. If her partner dies whenever she climaxes then that's four deaths every week. It's not even accidental murder after the second in my opinion.
MC: "Excuse me for a second. *ahem* LADIES"
Fairy squad assemble like they on stage and flamboyantly poses like JoJo characters with MC in the front with his hips afront, hand over his eyes and the other towards the camera.
He won't return to the future. He WON'T have a future if his grandma dies, since he's... You know, the child of her child. Meaning if she dies, her child won't be conceived, and neither will he.