The Missing Ache is a Keychain for Roxas's, Xion's, Player's, and Ventus's Keyblades that appears in Kingdom Hearts 358/2 Days and Kingdom Hearts Union χ. In Kingdom Hearts 358/2 Days, it can be upgraded to the Missing Ache+.
The Missing Ache's design differs depending on its upgrades, most of which are in Kingdom Hearts Union χ.
The default design has a black handle and neck, with the handle sporting two protrusions on either side that curve upward. The guard is comprised of two chartreuse spikes that curve downward. The teeth are also chartreuse and resemble the top half of the Nobody symbol, with two of the spikes being longer than the others. Missing Ache's Keychain token is chartreuse as well and has a shape similar to the handle, albeit squashed down. Unlike other Keyblades in Kingdom Hearts Union χ, it is this form of the Keychain that matches its depiction in other games.
The first upgrade retains the black handle, grip, and bottom protrusions. The guard is a chartreuse that fades into green, and resembles Roxas's zipper pull. The blade has a golden design in the middle, the tip vaguely resembling Sora's crown necklace. The teeth share the color scheme with the guard, but is now longer, has a black spike on one end, and a W-shaped black design on the other. The Keychain is shorter, and the tip has a spike.
The second upgrade bears a redesigned bottom. The protrusions are smaller, but bear beige spikes. The guard fades into cyan and resembles Larxene's knives, with a diamond in the center. The blade has V-shaped designs in the middle. The tip has a beige design at the very tip with a blue diamond in the center, which is also present in the teeth. The spikes in the teeth are wider, necessitating wider black designs. The Keychain's token resembles Roxas's zipper, but under the guard's color scheme. Ventus uses this upgrade in Kingdom Hearts Union χ.
The third upgrade envelopes the Keyblade in a green aura with lens flares near the guard and blade.
With this weapon equipped, Roxas's combo becomes a lunge, an uppercut swipe, a downward slash finished with a hilt slash. The aerial combo is a downward slash followed by a spinning slash.