Not likely. It falls under parody.
For future reference, that's not how parody defenses work under either US law or the Berne Convention. Even under US law, which is more permissive than Berne (due to national exemptions), the parody exemption (more properly one of the fair use exemptions) requires that the parody be specifically related to intrinsic properties of the underlying work such that the parody could not be applied to other similar works. In other words, just having the characters fuck does not make it a parody of Avatar.
The real exemption that basically all of these "parodies" fall under is the "not worth the hassle exemption," where a fan work that makes no real money isn't worth the time it takes a lawyer to sign into their email and send a pre-written cease and desist letter.
These VNs demo games are closest in copyright to Tijuana Bibles, which also sometimes tried to use parody exemptions and invariably lost. For anywhere without a specific national exemption to provide a very broad satire or parody carve-out, they are all infringing and unauthorized uses. Which should be an added incentive to make them good.