I had this germ of a story about three or four friends. One of them saw himself from the future in his washing machine, like a time window, telling him that something they did when they were kids broke the future (or another universe, I can't remember). So the story would change between when they were kids and did something that changed everything, the present where they're young adults struggling with life and the future (or various futures, more likely) where it's more of a sci fi action adventure, in a ruined world.
I had read 20th Century Boys three months before. Twice.
I tried to keep changing a little bit of the concept, but it was so heavily inspired I just dropped it (though now that I'm remembering it, I'm kinda tempted to give it another go)