The story of Kingdom Hearts has one of the longest-running coherent stories in gaming history, having ties to ten years prior to Kingdom Hearts 3D’s release in 2012 and across many games. Newcomers to the series are likely to be a bit uninformed by now, so I feel that I must summarize the story thus far.
Note that there are massive series spoilers here, and I have dramatically condensed the summaries, so you’ll probably find bunches of random notes popping up when they probably would’ve been better placed earlier. I did not cover every single thing, so note that; I just grabbed the major stuff out of my memories.
These are in the order of their plots in relevance to the series placement, not their actual release dates.