Citadel Law says:

"Plot: Kneel a Maester character to choose a player. That player must choose and reveal a new plot card."

Can this event be used in the Plot phase before the first plots of the game are chosen and revealed? The reason I question it is because Citadel Law says, "a new plot card," which makes me think that there has to be an "old" plot card already out.

Shadow Parasite says:

"Response: After a character's STR is reduced by X, Shadow Parasite gets +X STR until the end of the phase."

Can this response be triggered from a Flame-Kissed that was placed on a character before the Shadow Parasite comes into play? For example, the opponent plays Flame-Kissed on my 3-STR character during Turn 1. In turn 2 the opponent plays the Shadow Parasite and activates the Response because of Flame-Kissed's STR reduction. I don't think this works, but it was a question that came up in our play group.

"Citadel Law says:

"Plot: Kneel a Maester character to choose a player. That player must choose and reveal a new plot card."

Can this event be used in the Plot phase before the first plots of the game are chosen and revealed? The reason I question it is because Citadel Law says, "a new plot card," which makes me think that there has to be an "old" plot card already out."

There is a Player Action window after the beginning of the Plot phase, but before the choosing and revealing of plots, so I don't see why not. Perhaps "new" simply refers to a Plot card in your "unrevealed" pile.

"Shadow Parasite says:

"Response: After a character's STR is reduced by X, Shadow Parasite gets +X STR until the end of the phase."

Can this response be triggered from a Flame-Kissed that was placed on a character before the Shadow Parasite comes into play? For example, the opponent plays Flame-Kissed on my 3-STR character during Turn 1. In turn 2 the opponent plays the Shadow Parasite and activates the Response because of Flame-Kissed's STR reduction. I don't think this works, but it was a question that came up in our play group."

I would guess that "After" requires the Response to trigger at the point of initiation, rather than a constant effect afterward... but I'm a little fuzzy on that.

Shadow Parasite needs to be in play when the STR reduction happens in order to trigger.

Specifically, a card's STR is lowered/reduced when a new -X STR modifier is first applied. Once it has been applied, it does not create a continuing "after a character's STR is lowered" Response opportunity any more than the military challenge you won last round creates an "after you win a military challenge" Response opportunity this round.