Birdy started out as a homemade robot that Athrun Zala built and handed off to Kira Yamato in C.E. 68 right before heading back to PLANT. It was essentially a parting gift, and Kira treated it that way—the little robot became his link to Athrun and a constant companion. You'd usually spot Kira with Birdy perched on his shoulder, and the thing stayed with him through both major wars.
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