(It only has suit actors except the very last scene)
It started in a place with dead Kamen Riders: Baron, Kurokage, Marika, Sigurd, Duke and Overlords: Demushu, Redyue, (I think) Grinsha.
A man who looked similar to Sagara appeared and shows his power.
He wants to revive those dead ones so that they'll work/fight for him.
Suddenly Gaim arrives (Kiwami Arms) but the man defeats him, takes away Gaim's power/lockseeds and Gaim loses his memories.
Back to the real world: All the riders found themselves transformed, although they should not be able to.
First there were Gridon and Bravo, then Knuckle and also Gaim appear.
Sagara pops up too and explains that the man is something similar to him, calling him "Maja" (魔蛇, demonic snake?).
Redyue appears and they start fighting.
Zangetsu Shin and Ryugen come too.
Gaim gets one of the lockseeds back (from Ryugen) and he starts to remember a little, but he said he doesn't want to fight and runs away. Zangetsu follows him and tells him that Gaim used to "go the way he believes",
At some point Maja had transformed to black Gaim. Ryugen and the others went to Maja's place. There are Baron, Kurokage, Marika, Sigurd, Duke, and Overlords. They groups fight.
Gridon vs. Kurokage, where Gridon apologized and said that everything was his fault
Zack vs. Baron, at the end of the fight they both vanished as if they both got defeated from each other's attack (in the dust)
The fighting continues and Gaim joins them. He gets back more lockseeds and finally his memory is back completely.
Suddenly Baron appears. He had only pretended to follow Maja's orders.
In the end all (!!) Riders fight Maja together and they win.
There are short farewell scenes between Gridon & Kurokage, Baron & Zack, Gaim & Ryugen.
The last scenes has Kaito and Kouta talking. Kouta thanks Kaito for helping him. Kaito explains that he doesn't want thanks and he only can't see how someone gets defeated that had defeated (=is stronger than) him.
They were talking about this and that.
Sometimes when the actors were struggeling with what they wanted to say the audience went "cuuuuute". (especially Takasugi Mahiro and Shida Yuumi)
They had to say who is their favorite Kamen Rider, who they wanted to marry (from Gaim cast) and everyone did the henshin pose.
I don't remember everything....
Funny was how Sano Gaku said he wanted to marry Kobayashi Yutaka. Yutaka said that Gaku had already confessed to him in magazines before. Then Gaku said he misunderstood "kekkon" (marry) as some other word meaning "fight", so he chose Yutaka because he's weak.
Many of the actors and their characters were quite different, best example Yutaka and Kaito.
When Takasugi Mahiro did his henshin, he said "I'm finally a hero" and Sano Gaku said "I'll always be with Micchi". Gaku explained that he said it as an answer to Mahiro.
At the end Yutaka and Matsuda Gaku sang "Never Surrender" while dancing. Sano Gaku sang "Rise Up Your Flag" and did a row of backflips at the end.
Then everyone came on stage and thanked the audience for the support for the whole year.
Several of the actors said that it was thanks to Sano Gaku that the year/filming was so good so at the end Gaku started crying and couldn't really say much of a message.
I'll look up some Japanese reports and edit it...maybe. But I hope you enjoy reading this anyway ;)