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.

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.

Roxas and Xion can wield the Oathkeeper in Kingdom Hearts 358/2 Days by equipping the Zero Gear ⑤ with one Ability Unit.

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 wielded by Roxas in Kingdom Hearts 358/2 Days, the same charm turns azure and white. 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.

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. In Kingdom Hearts 358/2 Days, the Oathkeeper's combos are the exact same as the Two Become One Keyblade.