i need some idea for a level 100 campaign please share your ideas
Retire the characters to the status of largely passive arbiters of reality and start again.
I'm guessing that you got here by short cuts. Since it has taken me 3 years and roughly 200 hours of gaming to go from 1st-6th level, I can't imagine what a campaign that legitimately got to level 100 looks like, but I can tell you that it would need to met more than once weekly for 8 hours at a stretch since the beginning of 3e 13 or so years ago. 6000+ hours of gaming? I just can't fathom it.
Having spent 5 years playing a character between 7th and 13th level once, I just can't imagine the need for any story to need 100th level characters. It's easily possible to create defacto gods in 3e by 20th level, what are you going to do at 100th level? By the time you hit 60th level, there is really no plot possible that is big enough for your capabilities. Suitably optimized, the gods cringe at the thought of you and are awed by you. If the universe gets destroyed, at 100th level you probably can just recreate the whole thing.
The biggest problem with legitimate high level gaming is that the act of world creation necessary to sustain it in an interesting fashion continues to exponentionally climb in scope. At low level, you can create a village and a dungeon and be done, the gradually add villages, dungeons, and cities until you have a setting. But at 100th level, the terrain is now whole universes.
I don't know: "Something keeps eating alternate realities at a very fast rate, and putting them all back into place would just drain too many player resources. Worse, at the current rate whatever it is will eventually eat all realities in which you were ever born, causing you to cease to have ever existed. Thwart the Eater of All before it consumes all time and space and causes everything to never have been."