The story behind this ASMR work is that your future girlfriend and her even further future wife version use a time machine to travel back in time and double team you to try and prevent a future where you get erectile dysfunction (hence the tags). Because surely, there exists no other possible use for a time machine.

I'm gonna hazard a guess that the reason MC has ED in the first place was because of his wife's sexual drive was too high...

What is the source there is no tag of it