Oathkeeper

The Oathkeeper is a Keychain for Sora's Keyblade introduced in . It also appears as half of Roxas's dual set of Keyblades alongside the Oblivion, and was transformed from his original Kingdom Key after Xion returned to Sora. The Oathkeeper is symbolic of Sora's memories of Kairi.

Development
Originally, the Oathkeeper was meant to have a paopu fruit as the Keychain's token.

Kingdom Hearts
The Oathkeeper is formed when Sora uses Kairi's Wayfinder as a Keychain. After rescuing her from Hollow Bastion, Kairi gives him the charm for luck in the Secret Waterway in Traverse Town.

Kingdom Hearts Chain of Memories
When Sora enters Castle Oblivion, 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.

Kingdom Hearts II
Although Sora continued to possess the Lucky Charm after awakening from his hibernation, he is not able to use the Oathkeeper until he returns to Twilight Town and learns where Kairi had been taken.

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.

In Kingdom Hearts III, the two white points in the teeth of the blade are now darkened. The heart shape next to it is now bigger and level with the teeth. The angel wings making the guard are now yellow and blue, matching the teeth. The heart shape at the bottom of the blade is now hollow.

When the Oathkeeper is summoned in Kingdom Hearts II, it emerges in a bright, yellowish-white light. When summoned in Kingdom Hearts III, it appears in sparklingly light and feathers.

The Oathkeeper's English name stems from its Keychain, Kairi's Wayfinder, being a reminder of Sora's promise to her. Its Japanese name, "Promise's Charm," also reflects this status.

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

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

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, the Oathkeeper's Clock abilities are the best defensive abilities among all the Keychains in the game.

In Kingdom Hearts III, the Oathkeeper has balanced magic and strength stats, and along with its MP Converter ability the Oathkeeper is slightly more geared towards magic than its counterpart the Oblivion.