Korolev said:
Even if it is Plagarism, good luck proving it. A lot creative works borrow from each other - there's very little new under the sun and if we crucified every single new bit of media that resembled something else, we'd be crucifying darn near everything.
I've never seen Kill La Kill and I've never read whatever Manga Ooshima claims it rips off of, but I've watched a lot of movies and I've read a lot of books and the thing Ooshima is complaining about - taking the basic premise and themes from a work of fiction and using parts of them to make a new work of art - is INCREDIBLY common. As common as dishwater.
Is Pacific Rim "plagiarizing" Evangelion? Are The Hunger Games "plagiarizing" Battle Royale? Is the recent Tomb Raider game "Plagiarizing" the Uncharted games? Are the Uncharted Games "plagiarizing" from the older tomb raider games?
Ooshima might be right that the creators of Kill la Kill saw his earlier work and decided to make something similar, but that is NOT plagiarism. At the very worst it's creatively bankrupt, but not evil and in reality it's usually a pretty standard, normal thing that artists do. Many, many great books, films, games and shows have used earlier works to inspire them.
As I said in another post the whole anime industry seems to be fairly incestuous to begin with. If I had to guess the guy making the complaints is probably upset over "Kill La Kill" because it's done by people he worked with, perhaps off the record, and he feels they are stealing his ideas. With something this basic it would be insane (as I've explained at great length) but there might be more to the story. If he plans to take this to court, it makes a degree of sense that he wouldn't be putting all his cards out in the public eye at this stage.
Inspiration and plagiarism are always a touchy subject in creative fields, especially ones that start out being very open, but then gradually become ruthlessly corporate with everyone hoarding every IP they can in order to get an edge over the competition. The increasing international success of anime seems to have actually made it a lot less pleasant of a business than it was a couple decades ago.
I'll also say that giant robots were around a long time before Evangelion, to really plagiarize that you'd basically need to use the gimmick of a living, organic, war machine being disguised as a robot, which is actually being piloted by a guy sitting in a cybernetic implant.... that's the "twist" that actually makes Evangelion unique, and as such it would actually be pretty defensible. People simply linking to machines and piloting them was around long before Evangelion. Indeed one of the reasons the term "mecha" exists is because originally it was intended to differentiate between a war machine simply piloted by someone, and one that the pilot merges with. The idea being that cybernetics is when you replace yourself with machines, where mecha is a method of enhancing yourself with machines using a temporary interface to become one with it. Cyberpunk fiction used to get into this difference, and it was a key concept in things like the original "Bubblegum Crisis" (going by expanded materials), the idea being that the Knight Sabers were so much better than the AD police, because they basically blended with their machines and they became an extension of their bodies when they used their suits, as opposed to the police mech pilots who were basically driving a humanoid car. RPGs like "Shadowrun" and "Cyberpunk" also used versions of this, albeit more based on the writings of western Cyberpunk writers to a similar effect, with "Riggers" basically using cybernetics to become one with their vehicles. "Pacific Rim" actually has more to worry about from other giant robot franchises (western and Japanese) than Evangelion if someone actually wanted to pursue it... which I doubt anyone will, because it might as well be public domain at this point.
When it comes to "Battle Royale" and "The Hunger Games" you might as well bring "Lord Of The Flies", "The Running Man", and "The Long Walk" (I think that was the name of it) into it, two of the three which happen to be Steven King's works I believe, and it occurred to me a while ago that he would be able to sue. "The Long Walk" being a story about a future in which the government forces a bunch of kids to walk and when they stumble or cannot go any further they shoot them, the survivor at the end pretty much gets massive rewards, it's a compulsory thing if I remember done for largely the same reasons as "The Hunger Games" or "Battle Royale". It's like someone took that premise, combined it with "The Running Man" to make it more political as opposed to being about the media, and turned it into a story (in "The Running Man" there were political overtones, but one thing you might remember in both the story and the movie... they weren't supposed to use political/military prisoners specifically because of what happened in the story when they did it anyway for ratings).
"Tomb Raider", "Uncharted" and their ilk are more or less safe. They are largely ripping off "Indiana Jones" which itself was ripping off tropes from vintage 30 and 40s era adventure stories. The ironic thing is that they set out to make "Indy" politically correct by having him recovering treasure for museums. Originally most of the similar pulp adventurers did it largely for their own reasons, like Lara or Nathan. In a pulp story for example some adventurer might say go heading out in the jungles to find a golden idol so he could sell it, or to just display in his trophy room (being already rich) to show off how awesome an adventurer they were. It really wasn't much about respect for cultures, or shared global history. The ironic thing is that at the time, the places that inspired these stories and had the real adventurers running around didn't much care either. One of the reasons why I have so little respect for restoring treasures to their "rightful" owners in Egypt and stuff, when in reality these nations were literally jumping all over each other to attract treasure hunting expeditions and such so they could make money off of them. I find a certain degree of irony in nations demanding things back, after they gladly took the money and assisted with the looting at the time... now they want the gold too? I've always kind of wanted to see some of these nations hit with a bill (adjusted for inflation and hefty interests) for the expenses of the expeditions that found this stuff before they can get anything back... but I'm getting off track more than usual.
None of this matters of course, I'm just rambling. I pretty much agree with you that when it comes to some things your just not going to come up with fair ownership of the idea at this point.