In Coded Mickey uses the Starseeker Keyblade, while he should be using the Kingdom Key D. Does anyone know why?

He had Star Seeker since BBS. He decided that he didn't need Kingdom Key Darkside anymore, since they didn't need it to open or shut KH anymore. So he chose to use his first Keyblade.

ya and its way proer and looks better too

Why using the kingdom key D with only bugs and heartless came from the Journal ? , it's just doesn't fit taking out his strongest keyblade everytime

Mickey has a preference to his Star Seeker. It was his first Keyblade, so he's been using it for about twelve years by Re:coded and it is stronger than Kingdom Key Darkside.

And all KKD is good for, is shutting and opening KH, since it's a Keyblade of Darkness. The only reasons he didn't use Star Seeker in KH1 and KH2 are because he needed KKD, and he left Star Seeker with Yen Sid, who pretty much gave it to Sora when he got his clothes and Valor Form, it being the second Keyblade he wielded. It is assumed that Sora gave it back to Mickey.

Because Star Seeker gives an extra point in magic.

No I dont think thats why. But anyway its more usefull.