Super Sentai Taisen is a 1995 story meant to explain how Gorenger and J.A.K.Q. became part of the Super Sentai legacy, and how Ninja Captor isn't.
It appears as though the Black Cross Führer has reincarnated himself in what remains of the Variblune, the old ship of the Gorengers'. He makes his presence known when he announces to the world that he will destroy the Earth's only defense: the Super Sentai, by using the Variblune to open a portal to the one place a Sentai Ranger can't go: The Grid, a database that holds all the Sentai Ranger's power. He promises to keep the Rangers safe, but only if they become loyal to him. All the Rangers around the Earth hear of this, and are confused on what to do, since they themselves do not know how to enter it. The first Sentai team, the Battle Fever, decide to destroy the Variblune before it can cross dimensions. Using their Battle Fever Robo, they attempt to destroy the Variblune, which fights back, and eventually defeats the Robo.
The Battle Fever team is almost destroyed by the Variblune, but it is driven off by the Varidreen and Sky Ace. The Gorenger and J.A.K.Q. come out, and have a theory for the Battle Fever team: they think the combined effort of their ships could open another portal to The Grid, which they can then intercept and destroy the Variblune. Akarenger holds out his hand to Battle Japan, who knocks it away, saying they don't need the help of non-Sentai teams. A fight almost breaks out between the two teams, which is stopped by Big One. The Battle Fever team walks away, saying they will never be one of them.
Meanwhile, a man stands in a quarry, waiting for the Variblune. He offers his soul in exchange for free access to The Grid. Black Cross Führer is about to steal his soul, until the man reveals himself to be Daisuke Izumo, a member of the Ninja Captor. He is then joined by six other people, and they transform into the Ninja Captors. The Variblune summons some Gorenger monsters, and is about to shoot at them, but he is stopped by the five Jusho Fighters, with the Kakurangers joining the Ninja Captors in fighting on foot. The Jusho Fighters are soon joined by the Captor's mecha, forcing it to flee. The twelve ninjas defeat the monsters on the ground.
Akarenger appears, and says he and the Captors go way back. He offers an alliance with the Kakurangers, but Battle Japan appears, and commands the Kakuranger not associate with the Non-Super Sentai teams. Battle Japan and Akarenger get into a fight, which is again stopped by Big One. He warns the teams that the Black Cross Führer is preparing to enter the grid. Begrudgingly, Battle Japan allows the Gorengers and J.A.K.Q. to help.
The Variblune enters the Grid, but it is confronted by all the previous Sentai teams, and the other 3 teams. It manages to evade all the attacks, but the Varidreen, Sky Ace, and Battle Fever Robo combine and destroy the Variblune. Outside the Grid, Battle Japan acknowledges the other teams as being worthy of the Super Sentai name, and he apologizes for his behavior.
As all the teams leave, it is revealed the Black Cross Führer survived the explosion. He is still in the Grid, and plans to destroy himself along with the Grid. The Captors see this, and with their mecha, they fly into the Grid. It is believed they stopped the Führer's explosion, but at the cost of their lives. The 18 teams salute the fallen ninjas.