Start with getting friendly with johnny through good dialogue picks in chippin in especially "let's do something about that" choice, the friendship meter needs to hit 70% for some interesting stuff later. Might wanna check that synergy meter in pause menu to track progress. You'll need the whole panam questline done for the aldecaldos route or finish up rogue's stuff including blistering love if you're thinking about going the afterlife way, though there's always the arasaka path if you're not big on side content.

When you hit nocturne op55n1, here's something cool - wait a full 5 minutes during that rooftop chat and you'll unlock a hidden path, but only if you've got that 70% johnny meter. The dlc throws in another option with reed and songbird if you manage to keep them both breathing. Everything comes down to those final mikoshi choices, and whether you brought along your romance partner affects those endings quite a bit.

Just remember you can always reload from that point of no return if you're not happy with how things turned out first time around.