Oathkeeper

The Oathkeeper (約束のお守り) is a Keychain for Sora's Keyblade which appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, Kingdom Hearts II, Kingdom Hearts 358/2 Days, and Kingdom Hearts Re:coded. It also appears as half of Roxas's dual set of Keyblades alongside the Oblivion, and was transformed from his original Kingdom Key after he absorbed Xion. Fundamentally, the Oathkeeper is symbolic of Sora's memories of Kairi.

Story
The Oathkeeper is formed when Sora uses Kairi's Wayfinder as a Keychain. After rescuing her from Hollow Bastion in Kingdom Hearts, Kairi gives him the charm for luck in the Secret Waterway in Traverse Town. When Sora enters Castle Oblivion in Kingdom Hearts: Chain of Memories, Naminé rewrites Sora's memories, replacing Kairi's Lucky Charm with what appears to be a trinket from herself. After Sora defeats the Darkside at Destiny Islands and speaks with Naminé, she reveals the truth, and the illusion is dispelled. Although Sora continued to possess the Lucky Charm throughout Kingdom Hearts II, he is not able to use the Oathkeeper until he returns to Twilight Town and learns where Kairi had been taken. In Kingdom Hearts Re:coded, Data-Sora obtains the Oathkeeper Keychain after he fought a hooded boy and learns the truth behind the mysterious message that appears on Jiminy's first journal.

Design
The Oathkeeper's shaft displays two hearts, and its handle bears two angel wings, contrasting the bat wings that comprise Oblivion's handle. The teeth are fashioned in the shape of the Kanji for "light" (光), corresponding to the Oblivion's kanji for "darkness". Its Keychain token is Kairi's Wayfinder, a star sewn together from Thalassa Shells. In Castle Oblivion, it is replaced by Naminé's trinket until the illusion over Sora's Thalassa Charm breaks. When it is summoned by the user, Oathkeeper emerges in a bright, yellowish-white light.

Other appearances
A limited edition Oathkeeper was released with four other Keyblades in a special Play Arts Figures accessory set, Play Arts Arms.

In the intro of Kingdom Hearts 3D: Dream Drop Distance, Roxas is shown dual wielding the Oathkeeper and Oblivion against Axel; Sora also wields the Oathkeeper against Xemnas, while Riku uses the Oblivion.

Gameplay
In Kingdom Hearts, the Oathkeeper has a decent reach and is well-balanced, making it an acceptable substitute for the Lionheart.

In Kingdom Hearts II, its ability of Form Boost makes it much more useful for leveling Sora's Drive Forms, rather than for regular battle.

In Kingdom Hearts 358/2 Days, this Keyblade's ground combo begins with a thrust forward, followed by a diagonal vertical strike from the right side, and continues with a lightning-fast rush consisting of a horizontal slash left, the same slash right, and a vertical downward slash and ending with a jump back and a rushing diagonal spinning slash. You can change the combo and end it after the first upward slash by pressing ; this will trigger a jump into the air and a slightly angled spinning slash. The aerial combo is a rush forward and two downward spinning slashes from either side.

In Kingdom Hearts Re:coded, Oathkeeper's Clock abilities are the best defensive abilities among all the Keychains in the game.