1. An installment in a video game series which can be skipped due to it's irrelevance to the rest of the series
So going by that.
Current Main games:
Kh1- obvious reasons
KH Com- introduces Namine, CO, the org, the reason Sora was asleep during a year, what happened to Riku and more
KH2- obvious reasons
KH BBS- Introduces the antagonist of the series and three important characters (who may or may not be part of the seven lights) who need to be saved and more.
KH Days- Introduces Xion and gives a lot of backstory on Roxas. Also reveals more info about the organization and how Roxas came to be as he was in kh2.
KH Coded- reveals that when a heartless and a nobody are defeated the somebody returns. In short, it explains Xehanort's return in KH3D. It also is revealed by Data Namine that Sora needs to save Aqua, Terra, Ventus, Axel, Roxas, Xion and Namine.
KH3D- I shouldn't have to explain this one.
Current side games:
Kingdom Hearts V-cast- This one has been confirmed to be non-canon to the rest of the series and introduces no new plot elements.
Kingdom Hearts mobile- This one didn't even have a story to my knowledge. It was just an avatar game with some minigames and costumes.
So going by that.
Current Main games:
Kh1- obvious reasons
KH Com- introduces Namine, CO, the org, the reason Sora was asleep during a year, what happened to Riku and more
KH2- obvious reasons
KH BBS- Introduces the antagonist of the series and three important characters (who may or may not be part of the seven lights) who need to be saved and more.
KH Days- Introduces Xion and gives a lot of backstory on Roxas. Also reveals more info about the organization and how Roxas came to be as he was in kh2.
KH Coded- reveals that when a heartless and a nobody are defeated the somebody returns. In short, it explains Xehanort's return in KH3D. It also is revealed by Data Namine that Sora needs to save Aqua, Terra, Ventus, Axel, Roxas, Xion and Namine.
KH3D- I shouldn't have to explain this one.
Current side games:
Kingdom Hearts V-cast- This one has been confirmed to be non-canon to the rest of the series and introduces no new plot elements.
Kingdom Hearts mobile- This one didn't even have a story to my knowledge. It was just an avatar game with some minigames and costumes.
There you go