How are you negating the choosing of a team affiliation? Choosing is a cost to play the card. Once paid, who cares where they are after that?
Also, just because something says non-ongoing plot twist, that does not mean it can negate the effect prior to the word Ongoing. An ongoing plot twist is a plot twist with the Ongoing icon on it. It doesn't matter whether or not the effect is before or after the Ongoing word.
In some of the previous examples, they there's a requirement that it targets a character; yet the examples refer to effects that "target" team affilliations or are non-targeting.
As a last note, the part of an Ongoing plot twist after the Ongoing word becomes active the moment the card is played (doesn't use the chain). Only the section before Ongoing uses the chain.
304.10 The text after the word "ongoing" describes the plot twist's ongoing powers. These powers do not follow the rules of playing effects. If the plot twist was played from hand, these powers do not produce any modifiers; if the plot twist was played from the resource row, these powers become active as the plot twist becomes "played" (after all the steps of playing it are done, but before a player receives priority). (See 505.1e.)
Example: Concrete Jungle reads, "Each of your opponents turns all locations he controls face down. <p> Ongoing: Whenever an opponent flips a location, that opponent discards a card." The ongoing triggered power is active once the plot twist is played, while the effect is still on the chain; the effect's modifier that turns the locations face down doesn't happen until the effect resolves. If an opponent flips a location in response to this plot twist, the ongoing triggered power will trigger off that.
So I flip a location (1).
I pass.
You flip Concrete Jungle.
You pass.
I flip another location (2).
I pass.
You pass.
Concrete Jungle's effect makes me discard for location (2).
We pass.
Both locations turn face down.
We pass.
Assuming, of course, that the locations had no effects and nothing else was played.
