Oathkeeper

The Oathkeeper (約束のお守り) is gained by speaking to Kairi in the Secret Waterway in Traverse Town, after her rescue in Kingdom Hearts. It has a decent reach and is well-balanced. It's 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. The Oathkeeper reappears in Kingdom Hearts II. The Oathkeeper is one of the two Keyblades Roxas uses, the other being the Oblivion. The first time Roxas is seen using Oathkeeper (Another Side, Another Story), it appears more metallic than Sora's. However this is only an effect applied during the High Quality cutscene. The Keychain motif is of Kairi's Lucky Charm; a Paopu fruit-like star for Sora, made of thalassa-shells, and Naminé's charm that was made of false memories for Roxas. 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". It can be seen as a Keyblade of light, to balance out Oblivion's darkness.

Power
Oathkeeper is one of the most demoted Keyblade's power. In Kingdom Hearts II, the power level is significantly decreased.

In Kingdom Hearts: Chain of Memories, the Oathkeeper card is obtained after completing Destiny Islands on the 12th floor.