There's always a beginning

Who: Gokudera and Yamamoto
When: The start of the end of the world.
What: The disease makes it to Namimori.

( Let's make sure it's not an end as well. )

Well no one can say we didn't try?

Who: Gokudera, Yamamoto, VONGOLA DEAR LORDS VONGOLA.
When: Late second trimester, after Yama's last baseball season.
What: Gokudera goes to pick up Yama after the season ends and they try to make a discreet stop over in Vegas.

( Eloping has gotten harder these days )