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, and Kingdom Hearts 358/2 Days. It also appears as half of Roxas's dual set of Keyblades alongside the Oblivion, and was transformed from his original Kingdom Key Roxas after he absorbed Xion. Fundamentally, the Oathkeeper is symbolic of Sora's memories of Kairi and Roxas's oath that he made to Xion.

The Oathkeeper is formed when Sora uses Kairi's Lucky Charm as a Keychain. Kairi originally gives him the charm at the Secret Waterway in Kingdom Hearts. After rescuing her from Hollow Bastion, Sora leaves her with his friends at Traverse Town so that he can go back to close the Door to Darkness, and Kairi gives him the charm for luck. When Sora enters Castle Oblivion in Kingdom Hearts: Chain of Memories, Naminé is forced to rewrite Sora's memory so that Kairi's Lucky Charm appears to be a trinket from herself, but after Sora defeats the Darkside at Destiny Islands and speaks with her, 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.

Design
The Oathkeeper's keychain token is Kairi's Lucky Charm, a star sewn together from Thalassa shells. Its 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". When it is summoned by the user, it 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.

Gameplay
The Oathkeeper has a decent reach and is well-balanced in Kingdom Hearts; Oathkeeper is a good substitute for the Lionheart, in case the player hasn't been able, or didn't want, to defeat Cloud and Leon in the Hades Cup. 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.