Musou Nargacuga

Opening

Narga's opening is the hardest one to get perfect. The fastest way to get both Obscurity stacks is PD'ing the first AND last hit of his nuke, that way his next attack will be the quick tail whip that you can PD for your second stack. Hitting the first PD is the important one. If you miss the last, he will do the fog into jump instead which you can PD for your second stack but its slower than the first option.

Twerk

This is the hardest move to avoid correctly especially with SW. Without rush up you need to be full stamina otherwise it will be impossible to avoid completely. It will also require an animation cancel.

Evade slash -> hop -> upslash cancel -> evade slash

You could also do: hop -> upslash cancel -> evade slash for the initial tail hits. He will also most likely turn around after his jump so use an adv. Slash to gain super armor through his turnaround if you're close to him.

Rain

Since SW doesn't allow you to block the rain your only option without Rush Up is to run outside the initial circle and roll into it right when it stops. If you have rush up you can block it and try to get as many PD's as possible. With PD(Lg) this would even be more dps if you pd the last instance but I need more testing to see if you can run it on Lg or not.

Single Trail

Just a small tip for this move. Evade slash right as he dashes behind you so you can do an upslash while turning and evade slash his jump again. This way the timing is consistent and you'll avoid any windpressure that could possibly hit you at the start of the dash.