Star Seeker

The Star Seeker is a Keychain for Sora's Keyblade and Mickey's Keyblade that is found in Kingdom Hearts Re:Chain of Memories, Kingdom Hearts II, Kingdom Hearts 358/2 Days, Kingdom Hearts coded, and Kingdom Hearts Birth by Sleep. In Kingdom Hearts 358/2 Days, it can be upgraded to the Star Seeker+.

Kingdom Hearts Birth by Sleep
Mickey wields this Keyblade throughout his Mark of Mastery. Following Terra-Xehanort's defeat, Mickey dejectedly returns the Star Seeker to Yen Sid, thinking he has failed, only for Yen Sid to give it back to him, revealing Mickey has passed.

Kingdom Hearts
Mickey wields the Star Seeker on his mission to locate the Kingdom Key D and seal the Door to Darkness. Once he finds the Kingdom Key D, he ceases using the Star Seeker for some time until after Xemnas's defeat.

Kingdom Hearts II
When Sora visits Flora, Fauna, and Merryweather to obtain his new clothes, he receives a copy of the Star Seeker as the Keyblade for his new Valor Form.

Kingdom Hearts coded
Mickey resumes using the Star Seeker during his mission to fix the bugs in Jiminy's Journal.

Design
The guard appears to be two shooting stars. The blade is blue and decorated with stars, while the teeth is a crescent moon and a star. Strangely, in Kingdom Hearts Birth by Sleep, King Mickey holds Star Seeker in reverse, with the opposite side of the Keyblade used as the teeth. The Keychain design is a crescent moon. The Keyblade's name seemingly references Mickey and Sora's journeys to the various worlds, which are seen as stars. It also makes a reference to the worlds in the universe of Kingdom Hearts, since stars refer to the worlds.

The Star Seeker is part of a group of weapons associated with the Mysterious Tower, along with the corresponding staff and shield. These weapons are decorated with crescent moons and stars, and are the second set of weapons available to the party.

Gameplay
King Mickey can equip this Keyblade in Kingdom Hearts 358/2 Days Mission Mode by equipping the Pandora's Gear. The ground combo for this weapon starts with a horizontal slash to the left, followed by a horizontal slash to the right, a spinning slash, and ends with a large jump to the left with a dashing slash back to the right.

The aerial combo consists of a horizontal slash to the right finishing with a vertical slash upward, followed by the upward slash leading into a 360° spin with the Keyblade held above the King's head, and ends with a series of three thrusts as he descends.

Final Fantasy XIII-2
Serah Farron's default bowsword is named Starseeker.

Notes and references
Stella