Retrokyu (レトロキュー) is spherical android handed over to Mirai Suenaga from a member of Genesis Frontier. Retrokyu follows Mirai wherever she goes and also transforms into the Retrograde Suit.
And here are the reference images for those of you who want to draw or build your own Retrokyu!
Retrokyu transforms into the retrograde suit.
Retrokyu is Mirai Suenaga's guardian and weapon in the story Mirai Millennium - the scenario will be released soon but in the meantime checkout the following anime sequence of Mirai Millennium which has been adapted for the OP for Culture Japan Season 2.
The OP is produced by JC Staff and Mirai Fusion.