Kingdom Hearts 4 is the newest game in the series.
Story
Spoiler warning : Plot and/or ending details follow.
In the beginning of the story, Sora comes across Riku and Yuffie battling for the Keystone Key. Yuffie has a weakness to darkness, and the two friends beat Riku and beat up the guards that were protecting the Keyblade. Sora and Riku travel to another world to summon the Keyblade, where they enter an ancient kingdom of Keyblade wielders, Keyblades born from darkness.
This one ended up much better:
Sora, Donald, and Goofy are back in Kingdom Hearts 4! The once and future king of the World-His Majesty, Riku, has perished while defending the Kingdom of Heart from a mysterious new threat. Sora, Donald, and Goofy set out on a search for the next king of the world. The sequel to the classic Kingdom Hearts will return to the world of 358/2 Days in Kingdom Hearts Re:coded. This time, however, Sora is called back into the fray as a member of the Royal Guard and he is joined by Donald and Goofy. After many more delightful events (and a dastardly Picnic feast in the Final Form), all the residents of the Land of Departure are reunited and the battle for Gimmick Tower begins.
Theme song
"Umi☆Ike" by Imai[3] is used during the island theme song.
Manga Adaptation
One Piece ONA: Tengen Toppa Gurren