Ultimate Chimeron is the thirteenth phase of the final boss. He is Roxas with the Organization coat bottom tattered and worn like a kilt, along with his black pants and boots. He is shirtless, has a large hole in his midsection due to Crisis Harley's final thrust, and has a organic-looking cord snaking from his neck to The World That Never Was. He has giant black wings as well. In the hole Kingdom Hearts is visible, and this is his weak point. Coltrane requires Holy Oblivion to deflect Chimeron's Keyblade strikes, wing beats and thorn beams. Chimeron is rooted to the "ground" (actually a small circle of invisible tiles) by more black cords. Coltrane is capable of flight during this battle, which is vital, for the fight takes place in interspace. The player must fly over to Chimeron, deflect 13 of his attacks, and use the Reaction Commands "Obliteration", "Strike!" (7 times), and "Keyslam" to take out roughly a bar of health. The player is pushed back, then pulled in again. The Reaction Command "Break Free!" ensues, followed by "Homing Reflect" and "Thorn Prison" to take out another 1/2 bar. Rinse and repeat! (20 bars of HP)

The music played during the battle is "Never Turn Back" by Crush 40.

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