Post S4 the world is apocalyptic and everyone is staying in facilities under strict military authority to survive the monsters from the Upside Down. The government decides to start early with repopulation efforts and have a random draft for women to become pregnant. Robin gets drafted and has a total breakdown so Eddie volunteers to take her place in getting pregnant (is stealth until now) Que Steve and Eddie getting paired together and have a month to conceive.
Bonus points for Steve so excited to be a dad but so sad and guilty for being excited since he knows Eddie didn't choose this.